{"gene":"PF3D7_MIT02300","run_date":"2026-09-08T15:24:04","timeline":{"discoveries":[{"year":1989,"finding":"The cytochrome b gene (CYTB) in Plasmodium gallinaceum was identified on a 6.2-kb multimeric extrachromosomal element. The amino acid translation showed significant similarity to cytochrome b sequences from yeast, mammal, and fungus. The CYTB transcript is part of a larger primary transcript that is subsequently processed, producing a 1.2-kb message. This was the first identification of a mitochondrial nucleic acid sequence in malaria-causing organisms, suggesting a functional cytochrome system exists in these parasites.","method":"Gene sequencing, Southern blotting, RNA analysis of extrachromosomal element","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct gene sequencing and transcript analysis in a single study with multiple orthogonal molecular methods","pmids":["2779560"],"is_preprint":false,"attribution":[{"species":"Plasmodium gallinaceum","strain":""}]},{"year":1993,"finding":"Sequencing the P. falciparum 6-kb mitochondrial element revealed that CYTB encodes one of only three proteins in the minimal mt genome. Structural analysis of the predicted CYTB protein showed that the critical quinone binding sites (Qo and Qi) are divergent from those of other species, consistent with resistance to antimycin and related inhibitors, and with increased affinity for 8-aminoquinolines and hydroxynaphthoquinones.","method":"DNA sequencing, comparative structural analysis, molecular modeling","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct sequencing and comparative structural analysis in single study; mechanistic inference from sequence divergence at quinone-binding sites","pmids":["8459834"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1993,"finding":"Inheritance of the CYTB gene from the mitochondrial 6-kb element is uniparental in P. falciparum. Analysis of 59 individual hybrid oocysts from a cross in the mosquito demonstrated that inheritance of CYTB was not biparental.","method":"Single base-pair polymorphism marker in CYTB used to track inheritance in 59 oocysts from a mosquito-stage cross","journal":"Current genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct genetic cross experiment with 59 individual oocysts, clear result replicated in subsequent study (PMID:7935632)","pmids":["8467535"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1994,"finding":"The uniparental inheritance of CYTB (mitochondrial 6-kb element) in malaria parasites is maternal. Purified male gametes of P. gallinaceum lacked hybridization signal for the 6-kb element probe, while female gametes were positive, demonstrating maternal transmission of the mitochondrial genome encoding CYTB.","method":"DNA hybridization of purified male and female gamete preparations with probes for 6-kb and 35-kb extrachromosomal DNAs","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct fractionation experiment on purified gametes with hybridization, two independent extrachromosomal genome probes, replicated finding from prior cross study","pmids":["7935632"],"is_preprint":false,"attribution":[{"species":"Plasmodium gallinaceum","strain":""}]},{"year":1999,"finding":"Mutations in P. berghei CYTB confer resistance to atovaquone. Three mutations were detected: M133I or L144S at the Qo1 site (extramembranous amphipathic helix) and V284F in the sixth transmembrane helix. V284F was present in all resistant clones; additional Qo1 mutations significantly increased resistance. These results establish that atovaquone targets the ubiquinol oxidase activity of the cytochrome bc1 complex through interaction with CYTB.","method":"In vivo selection of resistant clones by escalating atovaquone doses; cytochrome b gene sequencing of resistant clones","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct in vivo resistance selection combined with gene sequencing; multiple independent resistant clones; replicated in P. falciparum studies","pmids":["10593174"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":"ANKA"}]},{"year":2000,"finding":"Point mutations in P. falciparum CYTB are associated with atovaquone resistance. Single or double amino acid mutations (including M133I, G280D) were detected in parasites surviving atovaquone in vitro and in a patient with treatment failure. These mutations confer a 25- to 9,354-fold reduction in susceptibility. Molecular modeling showed resistance-associated mutations cluster around the putative atovaquone-binding site of CYTB, consistent with reduced binding affinity.","method":"In vitro selection at increasing atovaquone concentrations; gene sequencing; molecular modeling of atovaquone-CYTB interaction","journal":"Antimicrobial agents and chemotherapy","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro selection experiments plus clinical isolate sequencing plus molecular modeling; replicated across multiple labs","pmids":["10898682"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"K1"}]},{"year":2001,"finding":"A point mutation in the P. falciparum CYTB gene associated with atovaquone resistance results in altered respiratory function: atovaquone inhibited total oxygen consumption by up to 66% in sensitive parasites but only up to 28% in resistant parasites. The resistant isolate showed no change in sensitivity to the alternative pathway inhibitor salicylhydroxamic acid, indicating CYTB mutation specifically alters cytochrome pathway sensitivity without affecting the alternative respiratory pathway.","method":"Oxygen consumption measurements in isogenic sensitive and resistant P. falciparum clinical isolate pair; pharmacological dissection with atovaquone and salicylhydroxamic acid","journal":"Experimental parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct respirometry on isogenic parasite pair, single lab, two pharmacological agents","pmids":["11560411"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2002,"finding":"The double amino acid mutation M133I + G280D in P. falciparum CYTB, but not the single M133I mutation, is associated with a 5–9% loss of parasite fitness during erythrocytic stages in the absence of drug pressure. Molecular modeling predicted that G280D weakens the CYTB-ubiquinone complex due to proximity to the putative ubiquinone-binding site, reducing electron transport chain efficiency.","method":"Competitive growth fitness assay of atovaquone-resistant K1 clones with single vs. double CYTB mutations; molecular modeling of CYTB-ubiquinone interaction","journal":"Antimicrobial agents and chemotherapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct competitive fitness assay plus molecular modeling, single lab","pmids":["12121915"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"K1"}]},{"year":2005,"finding":"Atovaquone blocks the large-scale domain movement of the iron-sulfur protein (ISP) subunit required for electron transfer in the cytochrome bc1 complex by locking ISP in its CYTB-binding conformation. Site-directed mutagenesis of bacterial cytochrome b at its ef loop to more closely resemble Plasmodium CYTB increased sensitivity to atovaquone. A mutation within the ef loop corresponding to a malaria atovaquone-resistance mutation rendered the bacterial complex resistant to atovaquone and caused a 10-fold reduction in in vitro complex activity, providing direct proof that the ef loop mutation causes atovaquone resistance.","method":"Site-directed mutagenesis of bacterial (Rhodobacter capsulatus) cytochrome b; biophysical and biochemical measurements of ISP domain movement; in vitro cytochrome bc1 complex activity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution-level mutagenesis in bacterial surrogate system with rigorous biophysical/biochemical assays; multiple orthogonal methods; directly validates mechanism of Plasmodium CYTB resistance mutation","pmids":["15917236"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2007,"finding":"Mutations at the Qo2 domain of P. berghei CYTB (Y268N, Y268C, L271V, K272R) confer atovaquone resistance. These extend previously identified Qo1 mutations and converge on codon 268, mirroring the most common resistance mutations in P. falciparum CYTB, confirming Qo2 as a key atovaquone interaction site in CYTB.","method":"In vivo selection of P. berghei resistant strains; cytochrome b gene sequencing","journal":"Parasitology international","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct in vivo selection and sequencing; multiple independent mutant clones; single lab","pmids":["18248769"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2011,"finding":"In vitro evolution of decoquinate-resistant P. falciparum parasites revealed two nonsynonymous mutations (A122T and Y126C) in CYTB within helix C of the ubiquinol-binding pocket. Transgenic parasites expressing yeast dihydroorotate dehydrogenase were >200-fold less sensitive to decoquinate, confirming CYTB/mitochondrial electron transport chain as decoquinate's target. Molecular docking showed decoquinate and atovaquone have distinctly different binding modes within the ubiquinol-binding site of CYTB.","method":"In vitro resistance evolution; comparative genomic analysis; transgenic parasite complementation with yeast DHODH; molecular docking","journal":"ACS chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods including resistance genetics, transgenic complementation, and structural docking; single rigorous study","pmids":["21866942"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium yoelii","strain":""}]},{"year":2011,"finding":"The Y268C mutation in CYTB (equivalent to the atovaquone-resistance mutation) causes the conserved tyrosine residue to be replaced by cysteine, leading to cross-linking between cytochrome b and iron-sulfur subunits, increased ROS production, and oxidative disruption of the catalytic [2Fe-2S] cluster. This tyrosine residue is essential for controlling unproductive encounters between O2 and catalytic intermediates at the quinol oxidation site to prevent ROS generation.","method":"Site-directed mutagenesis of bacterial cytochrome b; biochemical assays of ROS production and enzyme activity; structural analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct mutagenesis reconstitution in bacterial system with biochemical ROS measurements; mechanistic insight directly applicable to Plasmodium CYTB resistance mutations","pmids":["21454570"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2012,"finding":"The Y268S mutation in P. falciparum CYTB (field isolate TM902CB) confers a 270-fold shift in atovaquone inhibitory constant (Ki), a ~40% reduction in Vmax of the bc1 complex, and a 3-fold increase in Km for decylubiquinol. Western blot analysis revealed reduced iron-sulfur protein (ISP) content in Y268S bc1, indicating weakened ISP-CYTB interaction. Gene expression analysis showed higher expression of bc1 and cytochrome c oxidase genes in the resistant strain, interpreted as compensation for reduced bc1 activity.","method":"Biochemical characterization of bc1 complex from atovaquone-resistant field isolate TM902CB; enzyme kinetics (Ki, Vmax, Km); Western blotting; gene expression analysis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical characterization of parasite bc1 complex with multiple orthogonal methods (kinetics, Western blot, gene expression) on a field isolate","pmids":["22282497"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"TM902CB"}]},{"year":2014,"finding":"Direct biochemical evidence that atovaquone inhibits the cytochrome bc1 complex through CYTB mutations in P. berghei. Using isolated mitochondria from P. berghei atovaquone-resistant clones, dihydroorotate-cytochrome c reductase activity was tested across atovaquone concentrations. Resistant clones carrying Y268C or Y268N CYTB mutations showed ~100-fold higher IC50 compared to sensitive clones (1.5–40 nM vs. 0.132–0.465 nM), providing the first direct biochemical evidence linking specific CYTB mutations to atovaquone resistance in the intact parasite.","method":"Mitochondrial isolation from P. berghei; DHO-cytochrome c reductase activity assay across atovaquone concentration range; comparison of IC50 between resistant clones and sensitive controls","journal":"Parasitology international","confidence":"High","confidence_rationale":"Tier 1 / Strong — first direct biochemical assay in isolated parasite mitochondria; multiple resistant clones tested; rigorous dose-response quantification","pmids":["25264100"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""}]},{"year":2014,"finding":"The reduction site (Qi site) of P. falciparum CYTB is a druggable antimalarial target. A novel macrocyclic inhibitor identified by diversity-oriented synthesis screening was shown by resistance selection and whole-genome sequencing to target the Qi site of CYTB. Combination of Qi site and Qo site inhibitors showed synergistic inhibition of P. falciparum.","method":"Whole-cell phenotypic screening; in vitro resistance selection; whole-genome sequencing; drug combination synergy assays","journal":"The Journal of infectious diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — resistance genetics and genome sequencing identify CYTB Qi site; synergy assay; single lab","pmids":["25336726"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"finding":"Compounds CK-2-68 and RYL-552, reported as PfNDH2 inhibitors, unexpectedly selected mutations at the Qo pocket of P. falciparum CYTB (including Y268S, M133I, K272R) in resistance selection experiments, not in PfNDH2. Molecular docking showed all three ETC inhibitors (including atovaquone) bind to the Qo pocket of CYTB, with Y268 forming strong van der Waals interactions with atovaquone's hydroxynaphthoquinone ring but not with the quinolone rings of the other compounds.","method":"In vitro resistance selection; whole-genome sequencing; molecular docking to CYTB Qo pocket","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — resistance genetics plus structural docking; single lab; identifies CYTB as unexpected target","pmids":["29844160"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"Dd2"},{"species":"Plasmodium falciparum","strain":"106/1"}]},{"year":2023,"finding":"WJM228, a 7-N-substituted-3-oxadiazole quinolone, targets the Qo site of P. falciparum CYTB. Forward genetic resistance studies revealed Qo site CYTB mutations confer resistance. In a biosensor assay, WJM228 was shown to impact the electron transport chain via inhibition of CYTB. The compound prevented pre-erythrocytic parasite and male gamete development and reduced asexual parasitemia in a P. berghei mouse model.","method":"Forward genetic resistance selection; whole-genome sequencing; mitochondrial biosensor assay; in vivo P. berghei mouse model","journal":"ACS infectious diseases","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic resistance mapping plus direct biosensor assay of ETC activity; in vivo model; single lab","pmids":["36853190"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":2024,"finding":"PyAz90, a pyrimidine azepine compound, targets P. falciparum cytochrome b (CYTB) as a molecular target. P. falciparum-resistant parasites generated in vitro carried mutations in CYTB, and in vitro assays of mitochondrial activity confirmed inhibition of the bc1 complex. PyAz90 blocked parasite transmission to mosquitoes at nanomolar concentrations and inhibited asexual parasite multiplication.","method":"In vitro resistance selection; gene sequencing; mitochondrial activity assays; transmission-blocking assays","journal":"JACS Au","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — resistance genetics plus direct mitochondrial assay; single lab; multiple biological readouts","pmids":["39483245"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"finding":"Gamhépathiopine, a thienopyrimidinone, inhibits the Qo site of P. falciparum CYTB (complex III of the electron transport chain). In vitro evolution of resistance and whole genome analysis identified mutations within the Qo site of CYTB. Biochemical assays confirmed direct inhibition of complex III activity. Exogenous expression of S. cerevisiae DHODH (rendering the ETC dispensable) completely abrogated gamhépathiopine activity, confirming CYTB/ETC dependence. Cross-resistance profiling and docking studies indicated a similar but not identical binding pose to atovaquone.","method":"In vitro resistance evolution; whole genome sequencing; biochemical complex III assay; transgenic Plasmodium with yeast DHODH; cross-resistance profiling; molecular docking","journal":"ACS infectious diseases","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods in single study: biochemical assay, transgenic complementation, resistance genetics, structural docking","pmids":["40460517"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"PF3D7_MIT02300 (CYTB) encodes the cytochrome b subunit of the mitochondrial cytochrome bc1 complex (complex III) in Plasmodium parasites; it is encoded on the minimal ~6-kb mitochondrial genome and maternally inherited; it functions as the catalytic core of the ubiquinol oxidation (Qo) and quinone reduction (Qi) sites, through which it accepts electrons from ubiquinol and passes them to the iron-sulfur protein subunit, maintaining the mitochondrial membrane potential and supporting de novo pyrimidine biosynthesis via DHODH; point mutations in its Qo site (particularly at codon 268, and also at codons 133, 144, 271, 272, 284) directly cause high-level atovaquone resistance by reducing drug binding affinity, impairing bc1 catalytic turnover, and weakening ISP-CYTB interaction, while incurring a measurable fitness cost; and the Qi site is also a druggable antimalarial target that synergizes with Qo-site inhibitors."},"narrative":{"mechanistic_narrative":"PF3D7_MIT02300 (CYTB) encodes the cytochrome b subunit of the mitochondrial cytochrome bc1 complex (complex III) in Plasmodium, one of only three protein-coding genes on the minimal ~6-kb extrachromosomal mitochondrial element and the first mitochondrial sequence identified in malaria parasites [PMID:2779560, PMID:8459834]. The gene is maternally inherited: single-oocyst analysis of mosquito-stage crosses showed uniparental transmission [PMID:8467535], and hybridization of purified P. gallinaceum gametes localized the 6-kb element to female but not male gametes [PMID:7935632]. Catalytically, CYTB accepts electrons from ubiquinol at its quinol oxidation (Qo) site and relays them via the iron-sulfur protein (ISP) subunit, whose large-scale domain movement between CYTB-binding conformations is required for turnover; atovaquone acts by locking ISP in its CYTB-binding conformation [PMID:15917236]. This activity is central to the mitochondrial cytochrome pathway of respiration, which CYTB mutations specifically perturb without affecting the salicylhydroxamic-acid-sensitive alternative pathway [PMID:11560411]. CYTB is the molecular target of atovaquone and a broad set of other electron-transport-chain inhibitors: Qo-site point mutations — recurrently converging on codon 268 (Y268S/N/C) and including M133I, L144S, G280D, L271V, K272R, V284F — confer high-level resistance by reducing inhibitor binding affinity, lowering bc1 catalytic Vmax, raising Km for ubiquinol, and weakening the ISP–CYTB interaction, at a measurable fitness cost during erythrocytic growth [PMID:10593174, PMID:10898682, PMID:18248769, PMID:22282497, PMID:12121915]. The conserved Qo-site tyrosine (Y268) both mediates strong van der Waals contact with atovaquone's hydroxynaphthoquinone ring and normally suppresses ROS generation, such that its mutation causes cytochrome b–ISP cross-linking, oxidative damage to the [2Fe-2S] cluster, and elevated ROS [PMID:21454570, PMID:29844160]. Dependence on CYTB/ETC function is demonstrable by rescue with yeast DHODH, which renders parasites insensitive to CYTB inhibitors [PMID:21866942, PMID:40460517]. Beyond the Qo site, the quinone reduction (Qi) site of CYTB is an independent druggable target that synergizes with Qo-site inhibitors [PMID:25336726].","teleology":[{"year":1989,"claim":"Establishing that malaria parasites carry a mitochondrial cytochrome b sequence answered whether these organisms possess a functional cytochrome system at all.","evidence":"Gene sequencing and transcript analysis of a 6.2-kb extrachromosomal element in P. gallinaceum","pmids":["2779560"],"confidence":"Medium","gaps":["Function of the encoded protein not directly tested","Catalytic activity inferred from sequence similarity only"],"attribution":[{"species":"Plasmodium gallinaceum","strain":""}]},{"year":1993,"claim":"Sequencing the minimal P. falciparum mitochondrial genome placed CYTB as one of only three encoded proteins and flagged its divergent quinone-binding sites as a potential drug-selectivity determinant.","evidence":"DNA sequencing and comparative structural modeling of the 6-kb element","pmids":["8459834"],"confidence":"Medium","gaps":["Drug affinity predictions not experimentally validated in this study","No functional assay of the Qo/Qi sites"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1994,"claim":"Genetic-cross and gamete-fractionation experiments settled the inheritance mode of the CYTB-bearing mitochondrial genome, showing it is uniparental and specifically maternal.","evidence":"SNP tracking across 59 oocysts and hybridization of purified male/female gametes","pmids":["8467535","7935632"],"confidence":"High","gaps":["Mechanism enforcing maternal exclusion of paternal mitochondria not addressed"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium gallinaceum","strain":""}]},{"year":2001,"claim":"Selecting atovaquone-resistant parasites and mapping mutations to CYTB identified the cytochrome bc1 complex's ubiquinol oxidase activity as the drug's target and defined resistance loci around the Qo site.","evidence":"In vivo/in vitro resistance selection, gene sequencing, molecular modeling, and respirometry in P. berghei and P. falciparum","pmids":["10593174","10898682","11560411"],"confidence":"High","gaps":["Structural basis of reduced binding inferred from modeling only at this stage","Direct enzymatic measurement of mutant bc1 not yet performed"],"attribution":[{"species":"Plasmodium berghei","strain":"ANKA"},{"species":"Plasmodium falciparum","strain":"K1"}]},{"year":2002,"claim":"A competitive-growth assay quantified the fitness cost of CYTB resistance mutations, showing that double Qo-site mutations impair electron transport and reduce erythrocytic-stage fitness in the absence of drug.","evidence":"Competitive growth assay of single vs. double CYTB mutants plus ubiquinone-interaction modeling","pmids":["12121915"],"confidence":"Medium","gaps":["Fitness cost measured in vitro only","Molecular basis of impaired electron transport modeled, not measured"],"attribution":[{"species":"Plasmodium falciparum","strain":"K1"}]},{"year":2005,"claim":"A bacterial reconstitution system provided direct mechanistic proof that atovaquone works by locking the ISP subunit against CYTB and that a Plasmodium-type ef-loop mutation causes resistance with a catalytic penalty.","evidence":"Site-directed mutagenesis of Rhodobacter cytochrome b with biophysical ISP-movement and bc1 activity assays","pmids":["15917236"],"confidence":"High","gaps":["Demonstrated in bacterial surrogate rather than Plasmodium enzyme","Not all Plasmodium resistance residues tested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2011,"claim":"Mechanistic dissection of the Y268 mutation revealed why the conserved Qo-site tyrosine is both a drug-contact residue and a guard against ROS, explaining the collateral oxidative damage of resistance mutations.","evidence":"Bacterial cytochrome b mutagenesis with ROS and enzyme-activity assays; decoquinate resistance genetics with yeast-DHODH complementation and docking","pmids":["21454570","21866942"],"confidence":"High","gaps":["ROS mechanism established in bacterial system","Distinct binding modes shown by docking, not co-structures"],"attribution":[{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium yoelii","strain":""}]},{"year":2014,"claim":"Direct biochemical assays on parasite bc1 complexes quantified how specific Qo-site mutations reduce catalytic turnover, raise ubiquinol Km, and weaken ISP retention, closing the loop from genetics to enzymology.","evidence":"Enzyme kinetics, Western blotting and expression analysis on a Y268S field isolate; DHO-cytochrome c reductase IC50 assays on isolated P. berghei mitochondria","pmids":["22282497","25264100"],"confidence":"High","gaps":["No high-resolution structure of the resistant Plasmodium complex","Compensatory upregulation inferred from expression correlation"],"attribution":[{"species":"Plasmodium falciparum","strain":"TM902CB"},{"species":"Plasmodium berghei","strain":""}]},{"year":2014,"claim":"Identification of a Qi-site inhibitor established that CYTB's quinone-reduction site is a second druggable pocket that synergizes with Qo-site inhibition.","evidence":"Whole-cell screening, resistance selection with whole-genome sequencing, and drug combination synergy assays","pmids":["25336726"],"confidence":"Medium","gaps":["Qi-site binding inferred from resistance mapping, not structural data","Synergy mechanism not resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2025,"claim":"A succession of new chemotypes confirmed CYTB as a recurrently exploited antimalarial target across life-cycle stages, distinguished by variant Qo binding poses and validated by ETC-dependence rescue.","evidence":"Resistance selection, whole-genome sequencing, mitochondrial biosensor/complex III assays, yeast-DHODH complementation, and transmission-blocking/in vivo models for WJM228, PyAz90, and gamhepathiopine","pmids":["29844160","36853190","39483245","40460517"],"confidence":"Medium","gaps":["Binding poses inferred from docking and cross-resistance rather than co-crystal structures","Full mutation-selectivity landscape across chemotypes incomplete"],"attribution":[{"species":"Plasmodium falciparum","strain":"Dd2"},{"species":"Plasmodium falciparum","strain":"106/1"},{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium berghei","strain":""}]},{"year":null,"claim":"A high-resolution experimental structure of the Plasmodium CYTB-containing bc1 complex bound to inhibitors, and the in vivo mechanism enforcing maternal inheritance of its mitochondrial genome, remain unresolved.","evidence":"No timeline discovery provides a Plasmodium CYTB co-structure or the molecular basis of uniparental transmission","pmids":[],"confidence":"Medium","gaps":["No atomic-resolution structure of the parasite complex","Inheritance mechanism uncharacterized","Interplay between resistance mutations and stage-specific fitness incompletely mapped"],"attribution":[]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["Mitochondrial cytochrome bc1 complex (complex III), catalytic cytochrome b subunit [#8, #12, #13]"],"partners":["IRON-SULFUR PROTEIN (ISP/RIESKE) SUBUNIT OF COMPLEX III [#8, #12]","UBIQUINOL/UBIQUINONE (SUBSTRATE AT QO AND QI SITES) [#7, #12, #14]"],"other_free_text":["Encoded on the minimal ~6-kb mitochondrial extrachromosomal element, one of only three protein-coding genes [#0, #1]","Maternally (uniparentally) inherited via the mitochondrial genome [#2, #3]","Molecular target of atovaquone and multiple other ETC inhibitors; Qo-site mutations (especially at codon 268; also M133I, L144S, G280D, L271V, K272R, V284F) confer resistance with a fitness cost [#4, #5, #7, #9, #12, #15]","Qi (quinone reduction) site is an independent druggable pocket that synergizes with Qo-site inhibitors [#14]","Conserved Qo-site tyrosine (Y268) contacts atovaquone and suppresses ROS; mutation causes cytochrome b–ISP cross-linking and oxidative [2Fe-2S] damage [#11, #15]","ETC dependence demonstrated by loss of inhibitor sensitivity upon expression of yeast DHODH [#10, #18]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"10898682","id":"PMC_10898682","title":"Mutations in Plasmodium falciparum cytochrome b that are associated with atovaquone resistance are located at a putative drug-binding site.","date":"2000","source":"Antimicrobial agents and chemotherapy","url":"https://pubmed.ncbi.nlm.nih.gov/10898682","citation_count":299,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"9106361","id":"PMC_9106361","title":"Extrachromosomal DNA in the Apicomplexa.","date":"1997","source":"Microbiology and molecular biology reviews : 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transmission.","date":"2019","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/30814727","citation_count":109,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"20616281","id":"PMC_20616281","title":"A molecular clock for malaria parasites.","date":"2010","source":"Science (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/20616281","citation_count":102,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"19402894","id":"PMC_19402894","title":"Towards high-throughput molecular detection of Plasmodium: new approaches and molecular markers.","date":"2009","source":"Malaria 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(Haemosporida, Plasmodiidae) in golden tegu lizards: shedding light on a long-standing Haemosporida taxonomic puzzle.","date":"2025","source":"Parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/40152306","citation_count":1,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["CYTB"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"41049327","id":"PMC_41049327","title":"Hidden Plasmodium diversity revealed in southeastern Asian passerines using next-generation amplicon sequencing.","date":"2025","source":"Current research in parasitology & vector-borne diseases","url":"https://pubmed.ncbi.nlm.nih.gov/41049327","citation_count":1,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"40460517","id":"PMC_40460517","title":"The Thienopyrimidinone Gamhépathiopine Targets the QO Site of Plasmodium falciparum Cytochrome b.","date":"2025","source":"ACS infectious diseases","url":"https://pubmed.ncbi.nlm.nih.gov/40460517","citation_count":1,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"40218350","id":"PMC_40218350","title":"The Prevalence and Genetic Diversity of Avian Malaria in Wild Birds in the Republic of Korea.","date":"2025","source":"Animals : an open access journal from MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/40218350","citation_count":1,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"40867741","id":"PMC_40867741","title":"Molecular Screening of Plasmodium spp. in Free-Living Ring-Tailed Coatis (Nasua nasua) and Nine-Banded Armadillos (Dasypus novemcinctus) in the Peruvian Amazon.","date":"2025","source":"Animals : an open access journal from MDPI","url":"https://pubmed.ncbi.nlm.nih.gov/40867741","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["CYTB"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"41216928","id":"PMC_41216928","title":"Feeding Preferences of Mosquitoes (Culicidae) from the Eastern Balkans and Their Role in Transmission of Avian Malaria.","date":"2025","source":"Integrative zoology","url":"https://pubmed.ncbi.nlm.nih.gov/41216928","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"41055323","id":"PMC_41055323","title":"Molecular detection of avian parasites in Australian mosquitoes (Culicidae).","date":"2025","source":"Journal of medical entomology","url":"https://pubmed.ncbi.nlm.nih.gov/41055323","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"38820542","id":"PMC_38820542","title":"Molecular prevalence, phylogeny and hematological impact of Toxoplasma gondii and Plasmodium spp. in common quails from Punjab, Pakistan.","date":"2024","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/38820542","citation_count":12,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":true,"competing_organism_match":"Toxoplasma","competing_organism_only":true},{"pmid":"39483245","id":"PMC_39483245","title":"Pyrimidine Azepine Targets the Plasmodium bc 1 Complex and Displays Multistage Antimalarial Activity.","date":"2024","source":"JACS Au","url":"https://pubmed.ncbi.nlm.nih.gov/39483245","citation_count":9,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["cytochrome b"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":41208,"output_tokens":5779,"usd":0.105154,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12999,"output_tokens":4792,"usd":0.092397,"stage2_stop_reason":"end_turn"},"total_usd":0.197551,"stage1_batch_id":"msgbatch_01S4WrhSkksYHeZXxqf3za3o","stage2_batch_id":"msgbatch_019VBBeuW6G52X8gZfsFDfb5","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1989,\n      \"finding\": \"The cytochrome b gene (CYTB) in Plasmodium gallinaceum was identified on a 6.2-kb multimeric extrachromosomal element. The amino acid translation showed significant similarity to cytochrome b sequences from yeast, mammal, and fungus. The CYTB transcript is part of a larger primary transcript that is subsequently processed, producing a 1.2-kb message. This was the first identification of a mitochondrial nucleic acid sequence in malaria-causing organisms, suggesting a functional cytochrome system exists in these parasites.\",\n      \"method\": \"Gene sequencing, Southern blotting, RNA analysis of extrachromosomal element\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct gene sequencing and transcript analysis in a single study with multiple orthogonal molecular methods\",\n      \"pmids\": [\"2779560\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium gallinaceum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Sequencing the P. falciparum 6-kb mitochondrial element revealed that CYTB encodes one of only three proteins in the minimal mt genome. Structural analysis of the predicted CYTB protein showed that the critical quinone binding sites (Qo and Qi) are divergent from those of other species, consistent with resistance to antimycin and related inhibitors, and with increased affinity for 8-aminoquinolines and hydroxynaphthoquinones.\",\n      \"method\": \"DNA sequencing, comparative structural analysis, molecular modeling\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct sequencing and comparative structural analysis in single study; mechanistic inference from sequence divergence at quinone-binding sites\",\n      \"pmids\": [\"8459834\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"Inheritance of the CYTB gene from the mitochondrial 6-kb element is uniparental in P. falciparum. Analysis of 59 individual hybrid oocysts from a cross in the mosquito demonstrated that inheritance of CYTB was not biparental.\",\n      \"method\": \"Single base-pair polymorphism marker in CYTB used to track inheritance in 59 oocysts from a mosquito-stage cross\",\n      \"journal\": \"Current genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct genetic cross experiment with 59 individual oocysts, clear result replicated in subsequent study (PMID:7935632)\",\n      \"pmids\": [\"8467535\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"The uniparental inheritance of CYTB (mitochondrial 6-kb element) in malaria parasites is maternal. Purified male gametes of P. gallinaceum lacked hybridization signal for the 6-kb element probe, while female gametes were positive, demonstrating maternal transmission of the mitochondrial genome encoding CYTB.\",\n      \"method\": \"DNA hybridization of purified male and female gamete preparations with probes for 6-kb and 35-kb extrachromosomal DNAs\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct fractionation experiment on purified gametes with hybridization, two independent extrachromosomal genome probes, replicated finding from prior cross study\",\n      \"pmids\": [\"7935632\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium gallinaceum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Mutations in P. berghei CYTB confer resistance to atovaquone. Three mutations were detected: M133I or L144S at the Qo1 site (extramembranous amphipathic helix) and V284F in the sixth transmembrane helix. V284F was present in all resistant clones; additional Qo1 mutations significantly increased resistance. These results establish that atovaquone targets the ubiquinol oxidase activity of the cytochrome bc1 complex through interaction with CYTB.\",\n      \"method\": \"In vivo selection of resistant clones by escalating atovaquone doses; cytochrome b gene sequencing of resistant clones\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct in vivo resistance selection combined with gene sequencing; multiple independent resistant clones; replicated in P. falciparum studies\",\n      \"pmids\": [\"10593174\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"ANKA\"}]\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Point mutations in P. falciparum CYTB are associated with atovaquone resistance. Single or double amino acid mutations (including M133I, G280D) were detected in parasites surviving atovaquone in vitro and in a patient with treatment failure. These mutations confer a 25- to 9,354-fold reduction in susceptibility. Molecular modeling showed resistance-associated mutations cluster around the putative atovaquone-binding site of CYTB, consistent with reduced binding affinity.\",\n      \"method\": \"In vitro selection at increasing atovaquone concentrations; gene sequencing; molecular modeling of atovaquone-CYTB interaction\",\n      \"journal\": \"Antimicrobial agents and chemotherapy\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro selection experiments plus clinical isolate sequencing plus molecular modeling; replicated across multiple labs\",\n      \"pmids\": [\"10898682\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"K1\"}]\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"A point mutation in the P. falciparum CYTB gene associated with atovaquone resistance results in altered respiratory function: atovaquone inhibited total oxygen consumption by up to 66% in sensitive parasites but only up to 28% in resistant parasites. The resistant isolate showed no change in sensitivity to the alternative pathway inhibitor salicylhydroxamic acid, indicating CYTB mutation specifically alters cytochrome pathway sensitivity without affecting the alternative respiratory pathway.\",\n      \"method\": \"Oxygen consumption measurements in isogenic sensitive and resistant P. falciparum clinical isolate pair; pharmacological dissection with atovaquone and salicylhydroxamic acid\",\n      \"journal\": \"Experimental parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct respirometry on isogenic parasite pair, single lab, two pharmacological agents\",\n      \"pmids\": [\"11560411\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"The double amino acid mutation M133I + G280D in P. falciparum CYTB, but not the single M133I mutation, is associated with a 5–9% loss of parasite fitness during erythrocytic stages in the absence of drug pressure. Molecular modeling predicted that G280D weakens the CYTB-ubiquinone complex due to proximity to the putative ubiquinone-binding site, reducing electron transport chain efficiency.\",\n      \"method\": \"Competitive growth fitness assay of atovaquone-resistant K1 clones with single vs. double CYTB mutations; molecular modeling of CYTB-ubiquinone interaction\",\n      \"journal\": \"Antimicrobial agents and chemotherapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct competitive fitness assay plus molecular modeling, single lab\",\n      \"pmids\": [\"12121915\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"K1\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Atovaquone blocks the large-scale domain movement of the iron-sulfur protein (ISP) subunit required for electron transfer in the cytochrome bc1 complex by locking ISP in its CYTB-binding conformation. Site-directed mutagenesis of bacterial cytochrome b at its ef loop to more closely resemble Plasmodium CYTB increased sensitivity to atovaquone. A mutation within the ef loop corresponding to a malaria atovaquone-resistance mutation rendered the bacterial complex resistant to atovaquone and caused a 10-fold reduction in in vitro complex activity, providing direct proof that the ef loop mutation causes atovaquone resistance.\",\n      \"method\": \"Site-directed mutagenesis of bacterial (Rhodobacter capsulatus) cytochrome b; biophysical and biochemical measurements of ISP domain movement; in vitro cytochrome bc1 complex activity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution-level mutagenesis in bacterial surrogate system with rigorous biophysical/biochemical assays; multiple orthogonal methods; directly validates mechanism of Plasmodium CYTB resistance mutation\",\n      \"pmids\": [\"15917236\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Mutations at the Qo2 domain of P. berghei CYTB (Y268N, Y268C, L271V, K272R) confer atovaquone resistance. These extend previously identified Qo1 mutations and converge on codon 268, mirroring the most common resistance mutations in P. falciparum CYTB, confirming Qo2 as a key atovaquone interaction site in CYTB.\",\n      \"method\": \"In vivo selection of P. berghei resistant strains; cytochrome b gene sequencing\",\n      \"journal\": \"Parasitology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct in vivo selection and sequencing; multiple independent mutant clones; single lab\",\n      \"pmids\": [\"18248769\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"In vitro evolution of decoquinate-resistant P. falciparum parasites revealed two nonsynonymous mutations (A122T and Y126C) in CYTB within helix C of the ubiquinol-binding pocket. Transgenic parasites expressing yeast dihydroorotate dehydrogenase were >200-fold less sensitive to decoquinate, confirming CYTB/mitochondrial electron transport chain as decoquinate's target. Molecular docking showed decoquinate and atovaquone have distinctly different binding modes within the ubiquinol-binding site of CYTB.\",\n      \"method\": \"In vitro resistance evolution; comparative genomic analysis; transgenic parasite complementation with yeast DHODH; molecular docking\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods including resistance genetics, transgenic complementation, and structural docking; single rigorous study\",\n      \"pmids\": [\"21866942\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium yoelii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The Y268C mutation in CYTB (equivalent to the atovaquone-resistance mutation) causes the conserved tyrosine residue to be replaced by cysteine, leading to cross-linking between cytochrome b and iron-sulfur subunits, increased ROS production, and oxidative disruption of the catalytic [2Fe-2S] cluster. This tyrosine residue is essential for controlling unproductive encounters between O2 and catalytic intermediates at the quinol oxidation site to prevent ROS generation.\",\n      \"method\": \"Site-directed mutagenesis of bacterial cytochrome b; biochemical assays of ROS production and enzyme activity; structural analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct mutagenesis reconstitution in bacterial system with biochemical ROS measurements; mechanistic insight directly applicable to Plasmodium CYTB resistance mutations\",\n      \"pmids\": [\"21454570\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The Y268S mutation in P. falciparum CYTB (field isolate TM902CB) confers a 270-fold shift in atovaquone inhibitory constant (Ki), a ~40% reduction in Vmax of the bc1 complex, and a 3-fold increase in Km for decylubiquinol. Western blot analysis revealed reduced iron-sulfur protein (ISP) content in Y268S bc1, indicating weakened ISP-CYTB interaction. Gene expression analysis showed higher expression of bc1 and cytochrome c oxidase genes in the resistant strain, interpreted as compensation for reduced bc1 activity.\",\n      \"method\": \"Biochemical characterization of bc1 complex from atovaquone-resistant field isolate TM902CB; enzyme kinetics (Ki, Vmax, Km); Western blotting; gene expression analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical characterization of parasite bc1 complex with multiple orthogonal methods (kinetics, Western blot, gene expression) on a field isolate\",\n      \"pmids\": [\"22282497\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"TM902CB\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Direct biochemical evidence that atovaquone inhibits the cytochrome bc1 complex through CYTB mutations in P. berghei. Using isolated mitochondria from P. berghei atovaquone-resistant clones, dihydroorotate-cytochrome c reductase activity was tested across atovaquone concentrations. Resistant clones carrying Y268C or Y268N CYTB mutations showed ~100-fold higher IC50 compared to sensitive clones (1.5–40 nM vs. 0.132–0.465 nM), providing the first direct biochemical evidence linking specific CYTB mutations to atovaquone resistance in the intact parasite.\",\n      \"method\": \"Mitochondrial isolation from P. berghei; DHO-cytochrome c reductase activity assay across atovaquone concentration range; comparison of IC50 between resistant clones and sensitive controls\",\n      \"journal\": \"Parasitology international\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — first direct biochemical assay in isolated parasite mitochondria; multiple resistant clones tested; rigorous dose-response quantification\",\n      \"pmids\": [\"25264100\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The reduction site (Qi site) of P. falciparum CYTB is a druggable antimalarial target. A novel macrocyclic inhibitor identified by diversity-oriented synthesis screening was shown by resistance selection and whole-genome sequencing to target the Qi site of CYTB. Combination of Qi site and Qo site inhibitors showed synergistic inhibition of P. falciparum.\",\n      \"method\": \"Whole-cell phenotypic screening; in vitro resistance selection; whole-genome sequencing; drug combination synergy assays\",\n      \"journal\": \"The Journal of infectious diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — resistance genetics and genome sequencing identify CYTB Qi site; synergy assay; single lab\",\n      \"pmids\": [\"25336726\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Compounds CK-2-68 and RYL-552, reported as PfNDH2 inhibitors, unexpectedly selected mutations at the Qo pocket of P. falciparum CYTB (including Y268S, M133I, K272R) in resistance selection experiments, not in PfNDH2. Molecular docking showed all three ETC inhibitors (including atovaquone) bind to the Qo pocket of CYTB, with Y268 forming strong van der Waals interactions with atovaquone's hydroxynaphthoquinone ring but not with the quinolone rings of the other compounds.\",\n      \"method\": \"In vitro resistance selection; whole-genome sequencing; molecular docking to CYTB Qo pocket\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — resistance genetics plus structural docking; single lab; identifies CYTB as unexpected target\",\n      \"pmids\": [\"29844160\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"Dd2\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"106/1\"}]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"WJM228, a 7-N-substituted-3-oxadiazole quinolone, targets the Qo site of P. falciparum CYTB. Forward genetic resistance studies revealed Qo site CYTB mutations confer resistance. In a biosensor assay, WJM228 was shown to impact the electron transport chain via inhibition of CYTB. The compound prevented pre-erythrocytic parasite and male gamete development and reduced asexual parasitemia in a P. berghei mouse model.\",\n      \"method\": \"Forward genetic resistance selection; whole-genome sequencing; mitochondrial biosensor assay; in vivo P. berghei mouse model\",\n      \"journal\": \"ACS infectious diseases\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic resistance mapping plus direct biosensor assay of ETC activity; in vivo model; single lab\",\n      \"pmids\": [\"36853190\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PyAz90, a pyrimidine azepine compound, targets P. falciparum cytochrome b (CYTB) as a molecular target. P. falciparum-resistant parasites generated in vitro carried mutations in CYTB, and in vitro assays of mitochondrial activity confirmed inhibition of the bc1 complex. PyAz90 blocked parasite transmission to mosquitoes at nanomolar concentrations and inhibited asexual parasite multiplication.\",\n      \"method\": \"In vitro resistance selection; gene sequencing; mitochondrial activity assays; transmission-blocking assays\",\n      \"journal\": \"JACS Au\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — resistance genetics plus direct mitochondrial assay; single lab; multiple biological readouts\",\n      \"pmids\": [\"39483245\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Gamhépathiopine, a thienopyrimidinone, inhibits the Qo site of P. falciparum CYTB (complex III of the electron transport chain). In vitro evolution of resistance and whole genome analysis identified mutations within the Qo site of CYTB. Biochemical assays confirmed direct inhibition of complex III activity. Exogenous expression of S. cerevisiae DHODH (rendering the ETC dispensable) completely abrogated gamhépathiopine activity, confirming CYTB/ETC dependence. Cross-resistance profiling and docking studies indicated a similar but not identical binding pose to atovaquone.\",\n      \"method\": \"In vitro resistance evolution; whole genome sequencing; biochemical complex III assay; transgenic Plasmodium with yeast DHODH; cross-resistance profiling; molecular docking\",\n      \"journal\": \"ACS infectious diseases\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods in single study: biochemical assay, transgenic complementation, resistance genetics, structural docking\",\n      \"pmids\": [\"40460517\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"PF3D7_MIT02300 (CYTB) encodes the cytochrome b subunit of the mitochondrial cytochrome bc1 complex (complex III) in Plasmodium parasites; it is encoded on the minimal ~6-kb mitochondrial genome and maternally inherited; it functions as the catalytic core of the ubiquinol oxidation (Qo) and quinone reduction (Qi) sites, through which it accepts electrons from ubiquinol and passes them to the iron-sulfur protein subunit, maintaining the mitochondrial membrane potential and supporting de novo pyrimidine biosynthesis via DHODH; point mutations in its Qo site (particularly at codon 268, and also at codons 133, 144, 271, 272, 284) directly cause high-level atovaquone resistance by reducing drug binding affinity, impairing bc1 catalytic turnover, and weakening ISP-CYTB interaction, while incurring a measurable fitness cost; and the Qi site is also a druggable antimalarial target that synergizes with Qo-site inhibitors.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PF3D7_MIT02300 (CYTB) encodes the cytochrome b subunit of the mitochondrial cytochrome bc1 complex (complex III) in Plasmodium, one of only three protein-coding genes on the minimal ~6-kb extrachromosomal mitochondrial element and the first mitochondrial sequence identified in malaria parasites [#0, #1]. The gene is maternally inherited: single-oocyst analysis of mosquito-stage crosses showed uniparental transmission [#2], and hybridization of purified P. gallinaceum gametes localized the 6-kb element to female but not male gametes [#3]. Catalytically, CYTB accepts electrons from ubiquinol at its quinol oxidation (Qo) site and relays them via the iron-sulfur protein (ISP) subunit, whose large-scale domain movement between CYTB-binding conformations is required for turnover; atovaquone acts by locking ISP in its CYTB-binding conformation [#8]. This activity is central to the mitochondrial cytochrome pathway of respiration, which CYTB mutations specifically perturb without affecting the salicylhydroxamic-acid-sensitive alternative pathway [#6]. CYTB is the molecular target of atovaquone and a broad set of other electron-transport-chain inhibitors: Qo-site point mutations — recurrently converging on codon 268 (Y268S/N/C) and including M133I, L144S, G280D, L271V, K272R, V284F — confer high-level resistance by reducing inhibitor binding affinity, lowering bc1 catalytic Vmax, raising Km for ubiquinol, and weakening the ISP–CYTB interaction, at a measurable fitness cost during erythrocytic growth [#4, #5, #9, #12, #7]. The conserved Qo-site tyrosine (Y268) both mediates strong van der Waals contact with atovaquone's hydroxynaphthoquinone ring and normally suppresses ROS generation, such that its mutation causes cytochrome b–ISP cross-linking, oxidative damage to the [2Fe-2S] cluster, and elevated ROS [#11, #15]. Dependence on CYTB/ETC function is demonstrable by rescue with yeast DHODH, which renders parasites insensitive to CYTB inhibitors [#10, #18]. Beyond the Qo site, the quinone reduction (Qi) site of CYTB is an independent druggable target that synergizes with Qo-site inhibitors [#14].\",\n  \"teleology\": [\n    {\n      \"year\": 1989,\n      \"claim\": \"Establishing that malaria parasites carry a mitochondrial cytochrome b sequence answered whether these organisms possess a functional cytochrome system at all.\",\n      \"evidence\": \"Gene sequencing and transcript analysis of a 6.2-kb extrachromosomal element in P. gallinaceum\",\n      \"pmids\": [\"2779560\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Function of the encoded protein not directly tested\", \"Catalytic activity inferred from sequence similarity only\"],\n      \"attribution\": [{\"species\": \"Plasmodium gallinaceum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Sequencing the minimal P. falciparum mitochondrial genome placed CYTB as one of only three encoded proteins and flagged its divergent quinone-binding sites as a potential drug-selectivity determinant.\",\n      \"evidence\": \"DNA sequencing and comparative structural modeling of the 6-kb element\",\n      \"pmids\": [\"8459834\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Drug affinity predictions not experimentally validated in this study\", \"No functional assay of the Qo/Qi sites\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Genetic-cross and gamete-fractionation experiments settled the inheritance mode of the CYTB-bearing mitochondrial genome, showing it is uniparental and specifically maternal.\",\n      \"evidence\": \"SNP tracking across 59 oocysts and hybridization of purified male/female gametes\",\n      \"pmids\": [\"8467535\", \"7935632\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism enforcing maternal exclusion of paternal mitochondria not addressed\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium gallinaceum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Selecting atovaquone-resistant parasites and mapping mutations to CYTB identified the cytochrome bc1 complex's ubiquinol oxidase activity as the drug's target and defined resistance loci around the Qo site.\",\n      \"evidence\": \"In vivo/in vitro resistance selection, gene sequencing, molecular modeling, and respirometry in P. berghei and P. falciparum\",\n      \"pmids\": [\"10593174\", \"10898682\", \"11560411\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of reduced binding inferred from modeling only at this stage\", \"Direct enzymatic measurement of mutant bc1 not yet performed\"],\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"ANKA\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"K1\"}]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"A competitive-growth assay quantified the fitness cost of CYTB resistance mutations, showing that double Qo-site mutations impair electron transport and reduce erythrocytic-stage fitness in the absence of drug.\",\n      \"evidence\": \"Competitive growth assay of single vs. double CYTB mutants plus ubiquinone-interaction modeling\",\n      \"pmids\": [\"12121915\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Fitness cost measured in vitro only\", \"Molecular basis of impaired electron transport modeled, not measured\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"K1\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"A bacterial reconstitution system provided direct mechanistic proof that atovaquone works by locking the ISP subunit against CYTB and that a Plasmodium-type ef-loop mutation causes resistance with a catalytic penalty.\",\n      \"evidence\": \"Site-directed mutagenesis of Rhodobacter cytochrome b with biophysical ISP-movement and bc1 activity assays\",\n      \"pmids\": [\"15917236\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Demonstrated in bacterial surrogate rather than Plasmodium enzyme\", \"Not all Plasmodium resistance residues tested\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Mechanistic dissection of the Y268 mutation revealed why the conserved Qo-site tyrosine is both a drug-contact residue and a guard against ROS, explaining the collateral oxidative damage of resistance mutations.\",\n      \"evidence\": \"Bacterial cytochrome b mutagenesis with ROS and enzyme-activity assays; decoquinate resistance genetics with yeast-DHODH complementation and docking\",\n      \"pmids\": [\"21454570\", \"21866942\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ROS mechanism established in bacterial system\", \"Distinct binding modes shown by docking, not co-structures\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium yoelii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Direct biochemical assays on parasite bc1 complexes quantified how specific Qo-site mutations reduce catalytic turnover, raise ubiquinol Km, and weaken ISP retention, closing the loop from genetics to enzymology.\",\n      \"evidence\": \"Enzyme kinetics, Western blotting and expression analysis on a Y268S field isolate; DHO-cytochrome c reductase IC50 assays on isolated P. berghei mitochondria\",\n      \"pmids\": [\"22282497\", \"25264100\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of the resistant Plasmodium complex\", \"Compensatory upregulation inferred from expression correlation\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"TM902CB\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identification of a Qi-site inhibitor established that CYTB's quinone-reduction site is a second druggable pocket that synergizes with Qo-site inhibition.\",\n      \"evidence\": \"Whole-cell screening, resistance selection with whole-genome sequencing, and drug combination synergy assays\",\n      \"pmids\": [\"25336726\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Qi-site binding inferred from resistance mapping, not structural data\", \"Synergy mechanism not resolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A succession of new chemotypes confirmed CYTB as a recurrently exploited antimalarial target across life-cycle stages, distinguished by variant Qo binding poses and validated by ETC-dependence rescue.\",\n      \"evidence\": \"Resistance selection, whole-genome sequencing, mitochondrial biosensor/complex III assays, yeast-DHODH complementation, and transmission-blocking/in vivo models for WJM228, PyAz90, and gamhepathiopine\",\n      \"pmids\": [\"29844160\", \"36853190\", \"39483245\", \"40460517\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Binding poses inferred from docking and cross-resistance rather than co-crystal structures\", \"Full mutation-selectivity landscape across chemotypes incomplete\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"Dd2\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"106/1\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium berghei\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A high-resolution experimental structure of the Plasmodium CYTB-containing bc1 complex bound to inhibitors, and the in vivo mechanism enforcing maternal inheritance of its mitochondrial genome, remain unresolved.\",\n      \"evidence\": \"No timeline discovery provides a Plasmodium CYTB co-structure or the molecular basis of uniparental transmission\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No atomic-resolution structure of the parasite complex\", \"Inheritance mechanism uncharacterized\", \"Interplay between resistance mutations and stage-specific fitness incompletely mapped\"],\n      \"attribution\": []\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0008121\", \"supporting_discovery_ids\": [8, 12, 13, 18]},\n      {\"term_id\": \"GO:0009055\", \"supporting_discovery_ids\": [8, 12]},\n      {\"term_id\": \"GO:0006122\", \"supporting_discovery_ids\": [8, 12, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005743\", \"supporting_discovery_ids\": [13]},\n      {\"term_id\": \"GO:0005739\", \"supporting_discovery_ids\": [0, 1, 13]},\n      {\"term_id\": \"GO:0005750\", \"supporting_discovery_ids\": [8, 12]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0022904\", \"supporting_discovery_ids\": [6, 8, 13, 16]},\n      {\"term_id\": \"GO:0006207\", \"supporting_discovery_ids\": [10, 18]}\n    ],\n    \"complexes\": [\n      \"Mitochondrial cytochrome bc1 complex (complex III), catalytic cytochrome b subunit [#8, #12, #13]\"\n    ],\n    \"partners\": [\n      \"Iron-sulfur protein (ISP/Rieske) subunit of complex III [#8, #12]\",\n      \"Ubiquinol/ubiquinone (substrate at Qo and Qi sites) [#7, #12, #14]\"\n    ],\n    \"other_free_text\": [\n      \"Encoded on the minimal ~6-kb mitochondrial extrachromosomal element, one of only three protein-coding genes [#0, #1]\",\n      \"Maternally (uniparentally) inherited via the mitochondrial genome [#2, #3]\",\n      \"Molecular target of atovaquone and multiple other ETC inhibitors; Qo-site mutations (especially at codon 268; also M133I, L144S, G280D, L271V, K272R, V284F) confer resistance with a fitness cost [#4, #5, #7, #9, #12, #15]\",\n      \"Qi (quinone reduction) site is an independent druggable pocket that synergizes with Qo-site inhibitors [#14]\",\n      \"Conserved Qo-site tyrosine (Y268) contacts atovaquone and suppresses ROS; mutation causes cytochrome b–ISP cross-linking and oxidative [2Fe-2S] damage [#11, #15]\",\n      \"ETC dependence demonstrated by loss of inhibitor sensitivity upon expression of yeast DHODH [#10, #18]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_MIT02300","name":null,"product":"cytochrome b","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"CYTB","evaluation":null}