{"gene":"PF3D7_1149000","run_date":"2026-09-08T14:19:05","timeline":{"discoveries":[{"year":1992,"finding":"Pf332 (PF3D7_1149000) is encoded by a ~20 kb gene on chromosome 11 containing highly degenerate glutamic acid-rich repeats (32% Glu), and is exported from the parasite to the infected red blood cell membrane within large vesicle-like structures (~1 µm diameter), as shown by immunofluorescence with monospecific antibodies. The protein migrates at ~2500 kDa by Western blot and immunoprecipitation.","method":"Western blot, immunoprecipitation, confocal immunofluorescence microscopy, mung bean nuclease mapping, cDNA/genomic sequence analysis","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (IFA, Western, IP, sequence) in a single study; no independent replication of all findings","pmids":["1544579"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1994,"finding":"Pf332 is secreted from the parasite via a Brefeldin A-sensitive (classical Golgi) pathway and is transported to the erythrocyte membrane in association with Maurer's clefts. Brefeldin A treatment completely blocks export and causes accumulation of Pf332 within the parasite. Pf332 is first detected in young trophozoites at the parasitophorous vacuole membrane or as large vesicle-like structures in the erythrocyte cytoplasm, and reaches the erythrocyte surface at very late stages (42–46 h post-invasion).","method":"Monoclonal antibody-based immunofluorescence, immunoelectron microscopy, Brefeldin A pharmacological block, kinetic analysis during blood-stage development","journal":"Experimental parasitology","confidence":"High","confidence_rationale":"Tier 2 / Strong — pharmacological perturbation with Brefeldin A combined with immunoelectron microscopy and time-course IFA; findings replicated in subsequent studies","pmids":["7957750"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"finding":"Pf332 co-localizes with PfEMP1, PfExp-1, and PfSbpl within a continuous membrane network in the erythrocyte cytoplasm comprising tubovesicular membrane network, Maurer's clefts, and membrane whorls, consistent with a role in protein trafficking to the erythrocyte surface.","method":"Co-localization by light and electron microscopy using antibodies against Pf332, PfEMP1, PfExp-1, PfSbpl; vital staining with LysoSensor Green DND-153","journal":"European journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-localization by antibody staining and EM; functional consequence inferred but not directly tested for Pf332","pmids":["12868595"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2004,"finding":"Pf332 associates with the core of large multimeric vesicle (LMV) assemblies in the erythrocyte cytoplasm, while variant antigens RIFIN and PfEMP1 co-traffic at the outer rim of the same vesicle complexes. This places Pf332 within a common trafficking pathway for surface-bound variant antigens.","method":"Co-localization immunofluorescence of Pf332, RIFIN, PfEMP1 in freshly isolated and cultured P. falciparum; BODIPY-Ceramide lipid staining","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — antibody co-localization in multiple parasite strains; sub-compartmentalization described but not functionally validated for Pf332 directly","pmids":["14668007"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2008,"finding":"Deletion of Pf332 in transgenic P. falciparum parasites causes increased red blood cell rigidity, significantly reduced adhesion to CD36, decreased surface expression of PfEMP1 on infected erythrocytes, and dramatic morphological changes in Maurer's clefts. Truncated forms of Pf332 restore a normal adhesion profile and normal Maurer's cleft morphology but do not reverse hyperrigidity. These results establish that Pf332 modulates RBC rigidity and assists PfEMP1 transport to the iRBC surface via Maurer's clefts.","method":"Transgenic parasite engineering (deletion and truncation), micropipette aspiration (RBC deformability), adhesion assay to CD36, flow cytometry for surface PfEMP1, electron microscopy of Maurer's clefts","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean genetic deletion and truncation with multiple orthogonal phenotypic readouts (biophysics, adhesion, surface ligand expression, ultrastructure) in a single rigorous study","pmids":["18832660"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"The DBL-like domain of Pf332 was expressed recombinantly and its fold validated by disulfide bond pattern analysis, which conformed to the generic DBL domain pattern. Structural modeling revealed differences from the erythrocyte-binding alphaDBL domain of P. knowlesi Duffy-binding protein. Genetic deletion of Pf332 showed no effect on cytoadhesion or merozoite invasion, while truncation (but not full deletion) significantly altered infected erythrocyte deformability, suggesting Pf332 functions as an anchoring/scaffolding protein rather than a cytoadherence ligand.","method":"Recombinant protein expression, disulfide bond analysis, structural modeling, transgenic parasite construction (deletion and truncation), deformability assay, cytoadhesion assay, invasion assay","journal":"Molecular microbiology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — biochemical domain validation combined with genetic loss-of-function and multiple functional readouts; partially contradicts PMID:18832660 on adhesion phenotype (negative finding on cytoadhesion here)","pmids":["19007413"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"finding":"Pf332 is targeted to the ER by an internal hydrophobic sequence that, unlike a signal peptide, is not proteolytically removed, and unlike a canonical transmembrane segment, does not span the ER membrane. Instead, both termini of the hydrophobic sequence enter the ER lumen, forming an ER-lumenal intermediate that is a productive step in the export pathway to the erythrocyte.","method":"Cell-based topology assays in intact Plasmodium-infected cells, ER-retention sequence (KDEL receptor) tagging experiments, protease protection assay, biochemical fractionation","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — intact-cell topology experiments with orthogonal KDEL-retention approach; single lab study with novel mechanistic finding","pmids":["37000891"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"Pf332 (PF3D7_1149000) is a megadalton, glutamic acid-rich protein that is targeted to the ER via an internal non-cleaved hydrophobic sequence forming a lumenal intermediate, exported through a Brefeldin A-sensitive Golgi pathway, trafficked to the infected erythrocyte via Maurer's clefts (where it occupies the core of large vesicle complexes co-carrying PfEMP1 and RIFIN), and functions as a scaffolding/anchoring protein that maintains Maurer's cleft morphology, modulates the increased rigidity of infected red blood cells, and facilitates surface display of PfEMP1 to support CD36-mediated cytoadherence; its DBL-like domain adopts a canonical DBL fold but genetic evidence argues against a direct role in cytoadhesion or merozoite invasion."},"narrative":{"mechanistic_narrative":"Pf332 (PF3D7_1149000) is a megadalton, glutamic acid-rich exported protein of blood-stage Plasmodium falciparum that acts as a scaffolding/anchoring protein at the infected erythrocyte, maintaining Maurer's cleft morphology, modulating red cell rigidity, and supporting surface display of the cytoadherence ligand PfEMP1 [PMID:1544579, PMID:18832660]. It is trafficked from the parasite through a Brefeldin A-sensitive classical Golgi pathway and delivered to the erythrocyte via large vesicle-like structures associated with Maurer's clefts, reaching the erythrocyte surface only at very late stages of development [PMID:7957750]. Within the erythrocyte cytoplasm Pf332 occupies the core of large multimeric vesicle assemblies that co-carry PfEMP1 and RIFIN at their outer rim, placing it in a shared trafficking route for surface variant antigens [PMID:14668007]. Genetic deletion increases RBC rigidity, reduces CD36 adhesion, lowers surface PfEMP1, and distorts Maurer's clefts, while truncation restores adhesion and cleft morphology but not rigidity, indicating that distinct regions of the protein govern these functions [PMID:18832660]. Its DBL-like domain adopts a canonical DBL fold, but loss-of-function shows no role in cytoadhesion or merozoite invasion, arguing against a direct receptor-ligand function [PMID:19007413]. Pf332 enters the secretory pathway through an internal, non-cleaved hydrophobic sequence whose termini both enter the ER lumen to form a productive lumenal export intermediate [PMID:37000891].","teleology":[{"year":1992,"claim":"Establishing that Pf332 is a giant glutamic acid-rich protein exported into the infected erythrocyte defined it as a candidate host-cell-remodeling antigen rather than an intracellular parasite protein.","evidence":"Western blot, immunoprecipitation, immunofluorescence and sequence mapping of a ~20 kb chromosome 11 gene in P. falciparum","pmids":["1544579"],"confidence":"Medium","gaps":["Function of the protein at the erythrocyte membrane not tested","Trafficking route not resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":1994,"claim":"Defining the export route showed Pf332 uses a classical Golgi-dependent secretory pathway and transits via Maurer's clefts, situating it in the parasite's protein-export machinery.","evidence":"Monoclonal antibody IFA, immunoelectron microscopy, Brefeldin A block and developmental time-course in P. falciparum","pmids":["7957750"],"confidence":"High","gaps":["Molecular signal driving ER entry not identified","Cargo relationship to other exported proteins unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2003,"claim":"Co-localization with PfEMP1, PfExp-1 and PfSbp1 across a continuous erythrocyte membrane network implicated Pf332 in trafficking of surface-destined proteins.","evidence":"Antibody co-localization by light and electron microscopy plus vital staining in P. falciparum","pmids":["12868595"],"confidence":"Medium","gaps":["Functional consequence inferred, not tested for Pf332","Direct physical interactions not demonstrated"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2004,"claim":"Mapping Pf332 to the core of large multimeric vesicles with PfEMP1 and RIFIN at the rim refined its position within a common variant-antigen trafficking pathway.","evidence":"Co-localization immunofluorescence and BODIPY-ceramide staining in P. falciparum strain 3D7","pmids":["14668007"],"confidence":"Medium","gaps":["Sub-compartmentalization not functionally validated for Pf332","Mechanism of core targeting unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":"3D7"}]},{"year":2008,"claim":"Genetic deletion and truncation established causal roles for Pf332 in maintaining Maurer's cleft morphology, controlling RBC rigidity, and enabling PfEMP1 surface display and CD36 adhesion, and showed these functions map to separable regions of the protein.","evidence":"Transgenic deletion/truncation with micropipette aspiration, CD36 adhesion assay, surface-PfEMP1 flow cytometry and EM of Maurer's clefts in P. falciparum","pmids":["18832660"],"confidence":"High","gaps":["Molecular partners mediating cleft maintenance not identified","Mechanism linking Pf332 to rigidity unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"claim":"Biochemical validation of the DBL-like fold combined with loss-of-function assays reclassified Pf332 as a scaffolding/anchoring protein rather than a cytoadherence ligand.","evidence":"Recombinant expression, disulfide-bond analysis, structural modeling and transgenic deletion/truncation with cytoadhesion, invasion and deformability assays in P. falciparum","pmids":["19007413"],"confidence":"High","gaps":["Adhesion phenotype partially contradicts PMID:18832660","Native binding partner of the DBL-like domain unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"claim":"Defining the ER-targeting mechanism revealed that Pf332 relies on an internal, non-cleaved hydrophobic sequence that forms a lumenal intermediate, explaining how this signal-peptide-less giant protein enters the export pathway.","evidence":"Intact-cell topology assays, KDEL-retention tagging, protease protection and fractionation in P. falciparum","pmids":["37000891"],"confidence":"Medium","gaps":["Downstream translocation steps from ER not mapped","Single-lab finding of the lumenal intermediate"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"The direct molecular partners through which Pf332 anchors Maurer's clefts and modulates erythrocyte rigidity remain unidentified.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No biochemically defined interactome for Pf332","Mechanism connecting the DBL-like domain to scaffolding function unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["Core of large multimeric vesicle (LMV) assemblies co-carrying PfEMP1 and RIFIN [#3]"],"partners":["PFEMP1 (CO-TRAFFICKING AND SURFACE DISPLAY DEPENDENCY) [#3, #4]","RIFIN (CO-TRAFFICKING IN SAME VESICLE COMPLEXES) [#3]","PFEXP-1 AND PFSBP1 (CO-LOCALIZATION WITHIN ERYTHROCYTE MEMBRANE NETWORK) [#2]"],"other_free_text":["Megadalton glutamic acid-rich protein (~2500 kDa; 32% Glu) encoded on chromosome 11 [#0]","Deletion increases infected-RBC rigidity, reduces CD36 adhesion, lowers surface PfEMP1, and distorts Maurer's clefts; truncation restores adhesion and cleft morphology but not rigidity [#4]","DBL-like domain adopts a canonical DBL fold but is dispensable for cytoadhesion and merozoite invasion [#5]","ER entry via an internal non-cleaved hydrophobic sequence forming a lumenal export intermediate [#6]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"15939796","id":"PMC_15939796","title":"SURFIN is a polymorphic antigen expressed on Plasmodium falciparum merozoites and infected erythrocytes.","date":"2005","source":"The Journal of experimental 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erythrocytes.","date":"1992","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/1544579","citation_count":100,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["Pf332"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"12868595","id":"PMC_12868595","title":"Evidence for trafficking of PfEMP1 to the surface of P. falciparum-infected erythrocytes via a complex membrane network.","date":"2003","source":"European journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/12868595","citation_count":69,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["Pf332"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"18832660","id":"PMC_18832660","title":"Functional alteration of red blood cells by a megadalton protein of Plasmodium 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journal","url":"https://pubmed.ncbi.nlm.nih.gov/24044371","citation_count":61,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["DBL"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"10674682","id":"PMC_10674682","title":"Plasmodium falciparum parasites in French Guiana: limited genetic diversity and high selfing rate.","date":"1999","source":"The American journal of tropical medicine and hygiene","url":"https://pubmed.ncbi.nlm.nih.gov/10674682","citation_count":58,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["Pf332"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"14668007","id":"PMC_14668007","title":"Common trafficking pathway for variant antigens destined for the surface of the Plasmodium falciparum-infected erythrocyte.","date":"2004","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/14668007","citation_count":58,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["Pf332"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"9502607","id":"PMC_9502607","title":"Humoral response to Plasmodium falciparum Pf155/ring-infected erythrocyte surface antigen and Pf332 in three sympatric ethnic groups of Burkina Faso.","date":"1998","source":"The American journal of tropical medicine and hygiene","url":"https://pubmed.ncbi.nlm.nih.gov/9502607","citation_count":57,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["Pf332"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"22646809","id":"PMC_22646809","title":"Low antibodies against Plasmodium falciparum and imbalanced pro-inflammatory cytokines are associated with severe malaria in Mozambican children: a case-control study.","date":"2012","source":"Malaria journal","url":"https://pubmed.ncbi.nlm.nih.gov/22646809","citation_count":57,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["DBL"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"17587350","id":"PMC_17587350","title":"Fc gamma receptor IIa (CD32) polymorphism and antibody responses to asexual blood-stage antigens of Plasmodium falciparum malaria in Sudanese patients.","date":"2007","source":"Scandinavian journal of immunology","url":"https://pubmed.ncbi.nlm.nih.gov/17587350","citation_count":54,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["Pf332"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"12082132","id":"PMC_12082132","title":"Evolutionary relationships of conserved cysteine-rich motifs in adhesive molecules of malaria parasites.","date":"2002","source":"Molecular biology and evolution","url":"https://pubmed.ncbi.nlm.nih.gov/12082132","citation_count":50,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["DBL"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"8076613","id":"PMC_8076613","title":"Interchromosomal exchange of a large subtelomeric segment in a Plasmodium falciparum cross.","date":"1994","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/8076613","citation_count":48,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["Pf332"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"9271170","id":"PMC_9271170","title":"Comparative study of DNA-based immunization vectors: effect of secretion signals on the antibody responses in mice.","date":"1997","source":"FEMS immunology and medical 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pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/37000891","citation_count":4,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["Pf332"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":13837,"output_tokens":2356,"usd":0.038426,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":7748,"output_tokens":3245,"usd":0.059932,"stage2_stop_reason":"end_turn"},"total_usd":0.098358,"stage1_batch_id":"msgbatch_011BPjN2BL33F8cJXD1r7V7T","stage2_batch_id":"msgbatch_01Qwg6vP7qxkpL6Gsc7tajsb","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1992,\n      \"finding\": \"Pf332 (PF3D7_1149000) is encoded by a ~20 kb gene on chromosome 11 containing highly degenerate glutamic acid-rich repeats (32% Glu), and is exported from the parasite to the infected red blood cell membrane within large vesicle-like structures (~1 µm diameter), as shown by immunofluorescence with monospecific antibodies. The protein migrates at ~2500 kDa by Western blot and immunoprecipitation.\",\n      \"method\": \"Western blot, immunoprecipitation, confocal immunofluorescence microscopy, mung bean nuclease mapping, cDNA/genomic sequence analysis\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (IFA, Western, IP, sequence) in a single study; no independent replication of all findings\",\n      \"pmids\": [\"1544579\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Pf332 is secreted from the parasite via a Brefeldin A-sensitive (classical Golgi) pathway and is transported to the erythrocyte membrane in association with Maurer's clefts. Brefeldin A treatment completely blocks export and causes accumulation of Pf332 within the parasite. Pf332 is first detected in young trophozoites at the parasitophorous vacuole membrane or as large vesicle-like structures in the erythrocyte cytoplasm, and reaches the erythrocyte surface at very late stages (42–46 h post-invasion).\",\n      \"method\": \"Monoclonal antibody-based immunofluorescence, immunoelectron microscopy, Brefeldin A pharmacological block, kinetic analysis during blood-stage development\",\n      \"journal\": \"Experimental parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — pharmacological perturbation with Brefeldin A combined with immunoelectron microscopy and time-course IFA; findings replicated in subsequent studies\",\n      \"pmids\": [\"7957750\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Pf332 co-localizes with PfEMP1, PfExp-1, and PfSbpl within a continuous membrane network in the erythrocyte cytoplasm comprising tubovesicular membrane network, Maurer's clefts, and membrane whorls, consistent with a role in protein trafficking to the erythrocyte surface.\",\n      \"method\": \"Co-localization by light and electron microscopy using antibodies against Pf332, PfEMP1, PfExp-1, PfSbpl; vital staining with LysoSensor Green DND-153\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-localization by antibody staining and EM; functional consequence inferred but not directly tested for Pf332\",\n      \"pmids\": [\"12868595\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Pf332 associates with the core of large multimeric vesicle (LMV) assemblies in the erythrocyte cytoplasm, while variant antigens RIFIN and PfEMP1 co-traffic at the outer rim of the same vesicle complexes. This places Pf332 within a common trafficking pathway for surface-bound variant antigens.\",\n      \"method\": \"Co-localization immunofluorescence of Pf332, RIFIN, PfEMP1 in freshly isolated and cultured P. falciparum; BODIPY-Ceramide lipid staining\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — antibody co-localization in multiple parasite strains; sub-compartmentalization described but not functionally validated for Pf332 directly\",\n      \"pmids\": [\"14668007\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Deletion of Pf332 in transgenic P. falciparum parasites causes increased red blood cell rigidity, significantly reduced adhesion to CD36, decreased surface expression of PfEMP1 on infected erythrocytes, and dramatic morphological changes in Maurer's clefts. Truncated forms of Pf332 restore a normal adhesion profile and normal Maurer's cleft morphology but do not reverse hyperrigidity. These results establish that Pf332 modulates RBC rigidity and assists PfEMP1 transport to the iRBC surface via Maurer's clefts.\",\n      \"method\": \"Transgenic parasite engineering (deletion and truncation), micropipette aspiration (RBC deformability), adhesion assay to CD36, flow cytometry for surface PfEMP1, electron microscopy of Maurer's clefts\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean genetic deletion and truncation with multiple orthogonal phenotypic readouts (biophysics, adhesion, surface ligand expression, ultrastructure) in a single rigorous study\",\n      \"pmids\": [\"18832660\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The DBL-like domain of Pf332 was expressed recombinantly and its fold validated by disulfide bond pattern analysis, which conformed to the generic DBL domain pattern. Structural modeling revealed differences from the erythrocyte-binding alphaDBL domain of P. knowlesi Duffy-binding protein. Genetic deletion of Pf332 showed no effect on cytoadhesion or merozoite invasion, while truncation (but not full deletion) significantly altered infected erythrocyte deformability, suggesting Pf332 functions as an anchoring/scaffolding protein rather than a cytoadherence ligand.\",\n      \"method\": \"Recombinant protein expression, disulfide bond analysis, structural modeling, transgenic parasite construction (deletion and truncation), deformability assay, cytoadhesion assay, invasion assay\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — biochemical domain validation combined with genetic loss-of-function and multiple functional readouts; partially contradicts PMID:18832660 on adhesion phenotype (negative finding on cytoadhesion here)\",\n      \"pmids\": [\"19007413\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Pf332 is targeted to the ER by an internal hydrophobic sequence that, unlike a signal peptide, is not proteolytically removed, and unlike a canonical transmembrane segment, does not span the ER membrane. Instead, both termini of the hydrophobic sequence enter the ER lumen, forming an ER-lumenal intermediate that is a productive step in the export pathway to the erythrocyte.\",\n      \"method\": \"Cell-based topology assays in intact Plasmodium-infected cells, ER-retention sequence (KDEL receptor) tagging experiments, protease protection assay, biochemical fractionation\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — intact-cell topology experiments with orthogonal KDEL-retention approach; single lab study with novel mechanistic finding\",\n      \"pmids\": [\"37000891\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"Pf332 (PF3D7_1149000) is a megadalton, glutamic acid-rich protein that is targeted to the ER via an internal non-cleaved hydrophobic sequence forming a lumenal intermediate, exported through a Brefeldin A-sensitive Golgi pathway, trafficked to the infected erythrocyte via Maurer's clefts (where it occupies the core of large vesicle complexes co-carrying PfEMP1 and RIFIN), and functions as a scaffolding/anchoring protein that maintains Maurer's cleft morphology, modulates the increased rigidity of infected red blood cells, and facilitates surface display of PfEMP1 to support CD36-mediated cytoadherence; its DBL-like domain adopts a canonical DBL fold but genetic evidence argues against a direct role in cytoadhesion or merozoite invasion.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"Pf332 (PF3D7_1149000) is a megadalton, glutamic acid-rich exported protein of blood-stage Plasmodium falciparum that acts as a scaffolding/anchoring protein at the infected erythrocyte, maintaining Maurer's cleft morphology, modulating red cell rigidity, and supporting surface display of the cytoadherence ligand PfEMP1 [#0, #4]. It is trafficked from the parasite through a Brefeldin A-sensitive classical Golgi pathway and delivered to the erythrocyte via large vesicle-like structures associated with Maurer's clefts, reaching the erythrocyte surface only at very late stages of development [#1]. Within the erythrocyte cytoplasm Pf332 occupies the core of large multimeric vesicle assemblies that co-carry PfEMP1 and RIFIN at their outer rim, placing it in a shared trafficking route for surface variant antigens [#3]. Genetic deletion increases RBC rigidity, reduces CD36 adhesion, lowers surface PfEMP1, and distorts Maurer's clefts, while truncation restores adhesion and cleft morphology but not rigidity, indicating that distinct regions of the protein govern these functions [#4]. Its DBL-like domain adopts a canonical DBL fold, but loss-of-function shows no role in cytoadhesion or merozoite invasion, arguing against a direct receptor-ligand function [#5]. Pf332 enters the secretory pathway through an internal, non-cleaved hydrophobic sequence whose termini both enter the ER lumen to form a productive lumenal export intermediate [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 1992,\n      \"claim\": \"Establishing that Pf332 is a giant glutamic acid-rich protein exported into the infected erythrocyte defined it as a candidate host-cell-remodeling antigen rather than an intracellular parasite protein.\",\n      \"evidence\": \"Western blot, immunoprecipitation, immunofluorescence and sequence mapping of a ~20 kb chromosome 11 gene in P. falciparum\",\n      \"pmids\": [\"1544579\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Function of the protein at the erythrocyte membrane not tested\", \"Trafficking route not resolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Defining the export route showed Pf332 uses a classical Golgi-dependent secretory pathway and transits via Maurer's clefts, situating it in the parasite's protein-export machinery.\",\n      \"evidence\": \"Monoclonal antibody IFA, immunoelectron microscopy, Brefeldin A block and developmental time-course in P. falciparum\",\n      \"pmids\": [\"7957750\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular signal driving ER entry not identified\", \"Cargo relationship to other exported proteins unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Co-localization with PfEMP1, PfExp-1 and PfSbp1 across a continuous erythrocyte membrane network implicated Pf332 in trafficking of surface-destined proteins.\",\n      \"evidence\": \"Antibody co-localization by light and electron microscopy plus vital staining in P. falciparum\",\n      \"pmids\": [\"12868595\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence inferred, not tested for Pf332\", \"Direct physical interactions not demonstrated\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Mapping Pf332 to the core of large multimeric vesicles with PfEMP1 and RIFIN at the rim refined its position within a common variant-antigen trafficking pathway.\",\n      \"evidence\": \"Co-localization immunofluorescence and BODIPY-ceramide staining in P. falciparum strain 3D7\",\n      \"pmids\": [\"14668007\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Sub-compartmentalization not functionally validated for Pf332\", \"Mechanism of core targeting unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"3D7\"}]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Genetic deletion and truncation established causal roles for Pf332 in maintaining Maurer's cleft morphology, controlling RBC rigidity, and enabling PfEMP1 surface display and CD36 adhesion, and showed these functions map to separable regions of the protein.\",\n      \"evidence\": \"Transgenic deletion/truncation with micropipette aspiration, CD36 adhesion assay, surface-PfEMP1 flow cytometry and EM of Maurer's clefts in P. falciparum\",\n      \"pmids\": [\"18832660\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular partners mediating cleft maintenance not identified\", \"Mechanism linking Pf332 to rigidity unresolved\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Biochemical validation of the DBL-like fold combined with loss-of-function assays reclassified Pf332 as a scaffolding/anchoring protein rather than a cytoadherence ligand.\",\n      \"evidence\": \"Recombinant expression, disulfide-bond analysis, structural modeling and transgenic deletion/truncation with cytoadhesion, invasion and deformability assays in P. falciparum\",\n      \"pmids\": [\"19007413\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Adhesion phenotype partially contradicts PMID:18832660\", \"Native binding partner of the DBL-like domain unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Defining the ER-targeting mechanism revealed that Pf332 relies on an internal, non-cleaved hydrophobic sequence that forms a lumenal intermediate, explaining how this signal-peptide-less giant protein enters the export pathway.\",\n      \"evidence\": \"Intact-cell topology assays, KDEL-retention tagging, protease protection and fractionation in P. falciparum\",\n      \"pmids\": [\"37000891\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Downstream translocation steps from ER not mapped\", \"Single-lab finding of the lumenal intermediate\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The direct molecular partners through which Pf332 anchors Maurer's clefts and modulates erythrocyte rigidity remain unidentified.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No biochemically defined interactome for Pf332\", \"Mechanism connecting the DBL-like domain to scaffolding function unknown\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [4, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020030\", \"supporting_discovery_ids\": [1, 2, 3]},\n      {\"term_id\": \"GO:0005788\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"GO:0020036\", \"supporting_discovery_ids\": [1, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0046789\", \"supporting_discovery_ids\": [3, 4]},\n      {\"term_id\": \"GO:0006886\", \"supporting_discovery_ids\": [1, 2, 6]}\n    ],\n    \"complexes\": [\n      \"Core of large multimeric vesicle (LMV) assemblies co-carrying PfEMP1 and RIFIN [#3]\"\n    ],\n    \"partners\": [\n      \"PfEMP1 (co-trafficking and surface display dependency) [#3, #4]\",\n      \"RIFIN (co-trafficking in same vesicle complexes) [#3]\",\n      \"PfExp-1 and PfSbp1 (co-localization within erythrocyte membrane network) [#2]\"\n    ],\n    \"other_free_text\": [\n      \"Megadalton glutamic acid-rich protein (~2500 kDa; 32% Glu) encoded on chromosome 11 [#0]\",\n      \"Deletion increases infected-RBC rigidity, reduces CD36 adhesion, lowers surface PfEMP1, and distorts Maurer's clefts; truncation restores adhesion and cleft morphology but not rigidity [#4]\",\n      \"DBL-like domain adopts a canonical DBL fold but is dispensable for cytoadhesion and merozoite invasion [#5]\",\n      \"ER entry via an internal non-cleaved hydrophobic sequence forming a lumenal export intermediate [#6]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_1149000","name":null,"product":"antigen 332, DBL-like protein","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"Pf332","evaluation":null}