{"gene":"PF3D7_0501300","run_date":"2026-09-07T10:55:52","timeline":{"discoveries":[{"year":2000,"finding":"SBP1 (PF3D7_0501300) is an integral membrane protein of Maurer's clefts. Its carboxy-terminal domain, exposed in the erythrocyte cytoplasm, interacts with a 35 kDa erythrocyte skeletal protein, suggesting SBP1 participates in anchoring Maurer's clefts to the erythrocyte submembrane skeleton.","method":"Immunoprecipitation with hyperimmune sera, subcellular fractionation, immunofluorescence/immunoelectron microscopy, domain analysis","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, Co-IP/fractionation showing C-terminal domain interaction with 35 kDa erythrocyte protein, replicated across two observations but no mutagenesis or reconstitution","pmids":["11087921"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"finding":"Targeted gene disruption of SBP1 in P. falciparum prevents PfEMP1 from reaching the infected red blood cell surface, abolishing IRBC adhesion. PfEMP1 remains in Maurer's clefts and other Maurer's cleft proteins are unaffected, but Maurer's clefts no longer localize close to the cell periphery. Complementation with sbp1 restores PfEMP1 surface expression and adhesion, demonstrating SBP1 is essential for PfEMP1 translocation to the IRBC surface.","method":"Targeted gene disruption, complementation, immunofluorescence microscopy, cytoadherence assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal genetic rescue (KO + complementation) with defined cellular phenotype, multiple orthogonal readouts (adhesion, surface expression, cleft localization)","pmids":["16520384"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"finding":"SBP1 functions at the parasitophorous vacuole membrane to load PfEMP1 into Maurer's clefts during their formation. In the absence of SBP1, PfEMP1 fails to reach the IRBC surface and the dominant antibody response of malaria-exposed women to the IRBC surface is abolished.","method":"Gene disruption, live-cell imaging, immunofluorescence, antibody reactivity assays","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 / Strong — independent lab, gene disruption with defined mechanistic phenotype at the PVM, consistent with PMID:16520384","pmids":["17023587"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"finding":"Parasite protein phosphatase 1 (PP1) modulates the phosphorylation status of the amino-terminal domain of SBP1 within the lumen of Maurer's clefts, as shown by co-immunoprecipitation and inhibition studies. Hyperphosphorylation of SBP1 induced by a PP1 inhibitor (calyculin A) prevents merozoite release from the host cell, implicating PP1-mediated SBP1 phosphorylation in red blood cell rupture.","method":"Co-immunoprecipitation, pharmacological inhibition (calyculin A), phosphorylation assays","journal":"Cellular microbiology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, Co-IP plus pharmacological inhibition with functional phenotype, no direct mutagenesis of phosphosites","pmids":["16548885"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"finding":"The C-terminal cytoplasmic domain of SBP1 interacts with the human erythrocyte protein LANCL1, which is specifically recruited to the surface of Maurer's clefts in mature P. falciparum blood stages. This interaction was identified by co-immunoprecipitation and proposed to prevent premature rupture of the red blood cell.","method":"Co-immunoprecipitation, immunofluorescence microscopy, mass spectrometry identification of LANCL1","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, Co-IP with MS identification plus localization, single method for functional inference","pmids":["15811525"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"The transmembrane domain of SBP1 functions as an internal signal sequence for entry into the parasite's secretory pathway and transport to the parasite plasma membrane. Additional N-terminal domains, characterized by high negative net charge, are required for trafficking beyond the parasite plasma membrane to the Maurer's clefts; these domains affect protein solubility, membrane orientation, and subcellular localization.","method":"Domain deletion/mutation analysis, biochemical fractionation, immunofluorescence microscopy, topology assays","journal":"Traffic (Copenhagen, Denmark)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single lab, multiple domain constructs tested with biochemical and localization readouts, no in vitro reconstitution","pmids":["19054387"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"The N-terminal region and transmembrane domain of SBP1 can functionally replace the corresponding regions of the unrelated PEXEL-negative exported protein REX2 to direct export, demonstrating that these sequence features are shared among PEXEL-negative exported proteins and are sufficient for export when combined.","method":"Domain-swap chimera constructs, live-cell fluorescence microscopy, export assays","journal":"Molecular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single lab, domain-swap experiments with functional readout, but no mutagenesis of individual residues","pmids":["19170882"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"finding":"During conditional export experiments, SBP1 physically interacts with the molecular chaperone PfBiP during early export steps, before reaching the Maurer's clefts.","method":"Conditional aggregation domain (CAD) export system, co-immunoprecipitation, immunofluorescence","journal":"Cellular microbiology","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single Co-IP in a conditional system; interaction inferred from the export system rather than direct biochemical reconstitution","pmids":["18691247"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"finding":"Plasmepsin V does not cleave the N-terminal sequence of SBP1, demonstrating that SBP1 is exported via a PEXEL/Plasmepsin V-independent pathway.","method":"In vitro Plasmepsin V cleavage assays, N-terminal sequencing","journal":"Traffic (Copenhagen, Denmark)","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic assay establishing a negative result (no cleavage), single lab; negative result is mechanistically informative","pmids":["23387285"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"finding":"The C-terminal cytoplasmic domain of SBP1 binds directly and specifically to defined sub-domains of two major RBC membrane skeleton components, protein 4.1R and spectrin. These interactions serve as a mechanism to anchor Maurer's clefts to the RBC membrane skeleton. However, these interactions alone are necessary but not sufficient for PfEMP1 translocation to the RBC surface; the N-terminal lumenal domain of SBP1 also plays an essential but uncharacterized role.","method":"Recombinant protein pulldown, binding domain mapping, complementary loss-of-function analysis","journal":"Biochimica et biophysica acta","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, direct binding assays with domain mapping and functional inference from KO, but no in vitro reconstitution of full complex","pmids":["25883090"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"finding":"SBP1 is exported to the Maurer's clefts as a soluble form in the red cell cytoplasm in association with the parasite group II chaperonin PfTRiC. The domain of interaction with PfTRiC resides within the amino-terminal domain of SBP1. This pathway appears to be shared among multiple Maurer's cleft membrane proteins with different export motifs.","method":"Co-immunoprecipitation, domain mapping, immunofluorescence microscopy","journal":"Traffic (Copenhagen, Denmark)","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, Co-IP with domain mapping; interaction with PfTRiC shown biochemically but no in vitro reconstitution","pmids":["25615740"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"finding":"P. berghei orthologues of SBP1 and MAHRP1 are required for CD36-mediated adhesion of P. berghei-infected RBCs to endothelium and for sequestration and virulence in mice. Complementation of P. berghei SBP1 KO with P. falciparum SBP1 restores sequestration and virulence, demonstrating functional conservation of SBP1 between rodent and human malaria parasites.","method":"Gene knockout, complementation with P. falciparum orthologue, bioluminescence imaging, in vivo adhesion/sequestration assays","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Strong — cross-species complementation with KO and in vivo phenotypic rescue, multiple independent readouts","pmids":["27225796"],"is_preprint":false,"attribution":[{"species":"Plasmodium berghei","strain":""},{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"finding":"Genetic deletion of SBP1 leads to a dramatic reduction in antibody recognition of infected erythrocytes and in opsonic phagocytosis of IEs by human antibodies. The great majority of antibody epitopes on the IE surface are SBP1-dependent, establishing SBP1 as a critical component of the trafficking pathway for major surface antigens targeted by human immunity.","method":"Targeted gene deletion, flow cytometry, opsonic phagocytosis assays, multi-population antibody studies","journal":"Cellular and molecular life sciences : CMLS","confidence":"High","confidence_rationale":"Tier 2 / Strong — gene deletion with multiple orthogonal functional readouts across multiple parasite genetic backgrounds and human populations","pmids":["27193441"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"finding":"P. knowlesi SBP1 (PkSBP1) localizes to membranous structures analogous to Maurer's clefts (Sinton and Mulligan stipplings) in both monkey and human erythrocytes infected with P. knowlesi. When expressed in P. falciparum-infected erythrocytes, recombinant PkSBP1 co-localizes with PfSBP1 at Maurer's clefts, indicating conserved trafficking.","method":"Epitope-tagged transgenic parasites, immunofluorescence assay, immunoelectron microscopy","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, direct localization experiment in two host cell types plus cross-species co-localization","pmids":["27732628"],"is_preprint":false,"attribution":[{"species":"Plasmodium knowlesi","strain":""}]},{"year":2019,"finding":"A comprehensive SBP1 interactome was mapped using sensitive proteomics approaches in P. falciparum-infected erythrocytes, identifying numerous exported parasite proteins and host-parasite interactions associated with SBP1 intracellular trafficking and virulence, including MAL8P1.4 as a linked virulence factor.","method":"Proximity-based/affinity proteomics (co-IP + mass spectrometry), functional validation of interactors","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single lab, MS-based interactome with functional follow-up on selected interactors, comprehensive but not individually reconstituted","pmids":["31476617"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"At the early trophozoite (ring form) stage, SBP1 accumulates within electron-dense material (EDM) in the parasite cytoplasm and in the parasitophorous vacuolar space, before being transported to Maurer's clefts in the erythrocyte cytoplasm. This defines EDM as an intermediate compartment in SBP1's export pathway.","method":"Immunoelectron microscopy with specific anti-SBP1 antibodies","journal":"Parasitology international","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, direct ultrastructural localization at defined parasite stages; single method but specific spatial resolution","pmids":["31669509"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2017,"finding":"Two PHISTc subfamily proteins (PFD1140w and PF11_0503) interact with SBP1 in vitro. PFD1140w interacts simultaneously with both PfEMP1 (cytoplasmic tail) and SBP1 to form a tripartite complex in vitro.","method":"Recombinant protein pulldown, co-immunoprecipitation, in vitro binding assay","journal":"The FEBS journal","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, in vitro binding assays with recombinant proteins; no in-cell validation of the SBP1-PHIST interaction","pmids":["29155505"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2018,"finding":"PfJ23, a PEXEL-positive hyp16 family member, directly interacts with purified SBP1 and both co-localize in parasites. PfEMP1 cytoplasmic tail, PfJ23, and SBP1 can form a complex in vitro, suggesting PfJ23 may assist in export of PEXEL-negative proteins including SBP1.","method":"Recombinant protein pulldown, in vitro co-immunoprecipitation, co-localization by immunofluorescence","journal":"Pathogens and disease","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, in vitro interaction only, limited functional validation","pmids":["30576479"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2019,"finding":"The cytoplasmic domain of CBP2 (a 2TM exported protein) interacts in vitro with SBP1; this interaction is influenced by ATP binding of CBP2.","method":"In vitro recombinant protein binding assay","journal":"International journal of biological macromolecules","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single in vitro binding assay, no in-cell validation","pmids":["31356937"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"finding":"Using time-resolved proximity biotinylation (SBP1 fused to TurboID), two membrane-associated proteins were identified as pre-export (early) interactors of SBP1 at the parasite plasma membrane, one with a predicted translocon domain. Conditional knockdown of these candidates showed they are essential for asexual growth and localize to the host-parasite interface during early intraerythrocytic stages, suggesting a role in extracting membrane proteins from the parasite plasma membrane for export.","method":"TurboID proximity biotinylation, label-free quantitative proteomics, conditional knockdown, immunofluorescence","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single lab, time-resolved proximity proteomics plus conditional mutant phenotyping; novel mechanistic insight but pre-print-level validation of the translocon candidate","pmids":["37772444"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"finding":"SBP1 and MAHRP2, despite containing transmembrane segment-like hydrophobic sequences, assume a lumenal topology within the parasite secretory pathway (ER lumen) as a productive intermediate for protein export. Addition of a C-terminal ER-retention signal enhances but does not completely block retention of SBP1 in the parasite ER, indicating a sub-population adopts an ER-lumenal state during the export process.","method":"Epitope-tagged constructs, ER-retention signal fusion, immunofluorescence, biochemical topology assays in intact cells","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — single lab, multiple topology constructs with biochemical and imaging readouts; novel pathway finding but single lab","pmids":["37000891"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"finding":"SBP1 localizes to dot-like Maurer's cleft structures in the cytoplasm of gametocyte-infected erythrocytes (not only asexual stages). Co-immunoprecipitation and mass spectrometry show that SBP1 interacts with the molecular chaperones PfHSP70-1 and PfHSP70-x during gametocyte maturation.","method":"Immunofluorescence microscopy, co-immunoprecipitation, mass spectrometry","journal":"Parasitology international","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — single lab, Co-IP with MS identification and localization in gametocytes; two orthogonal methods but single lab","pmids":["38331312"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"SBP1 (PF3D7_0501300) is an integral Maurer's cleft membrane protein in P. falciparum that traffics through the parasite ER lumen and electron-dense material in the PV space before reaching erythrocyte-cytoplasmic Maurer's clefts; its transmembrane domain acts as an internal, non-cleaved signal for secretory pathway entry (independent of PEXEL/Plasmepsin V processing), while its N-terminal lumenal domain interacts with the chaperonin PfTRiC and HSP70s to facilitate export, and its C-terminal cytoplasmic domain anchors Maurer's clefts to the erythrocyte skeleton via direct binding to spectrin and protein 4.1R and to the host protein LANCL1; SBP1 is essential for the translocation of PfEMP1 from Maurer's clefts to the IRBC surface (functioning at the parasitophorous vacuole membrane during Maurer's cleft formation), and its phosphorylation state is regulated by a Maurer's cleft-resident PP1-type phosphatase, with this function conserved across Plasmodium species including P. berghei and P. knowlesi."},"narrative":{"mechanistic_narrative":"SBP1 (PF3D7_0501300) is an integral membrane protein of the Maurer's clefts in Plasmodium falciparum-infected erythrocytes that serves as a central component of the parasite's protein-export and cytoadherence machinery [PMID:11087921, PMID:16520384]. It is essential for translocation of the major virulence adhesin PfEMP1 from the Maurer's clefts to the infected-red-cell surface: gene disruption traps PfEMP1 in the clefts, abolishes IRBC adhesion, and mislocalizes the clefts away from the cell periphery, phenotypes reversed by complementation [PMID:16520384], with SBP1 acting at the parasitophorous vacuole membrane to load PfEMP1 into forming clefts [PMID:17023587]. Its transmembrane segment functions as an internal, non-cleaved signal directing entry into the secretory pathway independently of PEXEL/Plasmepsin V processing, while a high-net-charge N-terminal region is required for onward export to the clefts [PMID:19054387, PMID:23387285]. During export SBP1 transits an ER-lumenal state and electron-dense intermediate compartments in the parasitophorous vacuolar space before reaching the erythrocyte-cytoplasmic clefts [PMID:37000891, PMID:31669509], and its soluble transport is chaperone-assisted through the N-terminal domain via the group II chaperonin PfTRiC [PMID:25615740]. At the clefts, the C-terminal cytoplasmic domain anchors the structures to the erythrocyte membrane skeleton through direct binding to spectrin and protein 4.1R [PMID:25883090]. SBP1 function is conserved across Plasmodium: the P. berghei orthologue is required for CD36-mediated sequestration and virulence in vivo and is rescued by P. falciparum SBP1 [PMID:27225796]. By controlling surface display of adhesins, SBP1 governs the great majority of antibody-accessible epitopes on the infected-cell surface and opsonic phagocytosis by human antibodies [PMID:27193441].","teleology":[{"year":2000,"claim":"Establishing SBP1's physical identity and location answered where in the infected cell it acts and hinted at a structural anchoring role.","evidence":"Immunoprecipitation, fractionation and immuno-EM in P. falciparum showing an integral Maurer's cleft protein whose C-terminal domain binds a 35 kDa erythrocyte skeletal protein","pmids":["11087921"],"confidence":"Medium","gaps":["Identity of the 35 kDa partner not defined here","No functional demonstration of anchoring","No mutagenesis of the interacting domain"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2005,"claim":"Identifying a host erythrocyte binding partner for the cytoplasmic tail extended SBP1's role to host-protein recruitment at the cleft surface.","evidence":"Co-IP with mass-spec identification and immunofluorescence in P. falciparum showing the C-terminal domain binds human LANCL1 recruited to Maurer's clefts","pmids":["15811525"],"confidence":"Medium","gaps":["Functional role in preventing rupture inferred, not demonstrated","Single method for the functional claim","Binding not mapped to residues"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"claim":"Genetic ablation defined SBP1's essential cellular function — routing PfEMP1 to the IRBC surface — resolving whether SBP1 is structural or a trafficking determinant.","evidence":"Targeted disruption plus complementation with adhesion, surface-expression and cleft-localization readouts in P. falciparum; independent gene disruption localizing action to the PVM","pmids":["16520384","17023587"],"confidence":"High","gaps":["Molecular mechanism of PfEMP1 loading at the PVM unresolved","Direct PfEMP1-SBP1 contact not shown","How SBP1 positions clefts at the periphery unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2006,"claim":"Linking SBP1 phosphorylation to a Maurer's cleft phosphatase connected its N-terminal state to the timing of host-cell rupture.","evidence":"Co-IP and calyculin A inhibition in P. falciparum showing PP1 modulates N-terminal SBP1 phosphorylation and that hyperphosphorylation blocks merozoite release","pmids":["16548885"],"confidence":"Medium","gaps":["Phosphosites not mapped by mutagenesis","Direct causal link between SBP1 phosphorylation and rupture not isolated from PP1's other substrates","Pharmacological rather than genetic evidence"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2008,"claim":"Dissecting the export signals showed how SBP1 enters and traverses the secretory pathway, defining transferable determinants of PEXEL-negative export.","evidence":"Domain deletion/topology assays and domain-swap chimeras with REX2, plus a conditional-export CAD system in P. falciparum identifying transmembrane and N-terminal export determinants and a PfBiP interaction","pmids":["19054387","19170882","18691247"],"confidence":"Medium","gaps":["Individual residue requirements not resolved","PfBiP interaction rests on a single Co-IP in an artificial export system","Mechanism of membrane extraction not addressed"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2013,"claim":"A negative enzymatic result formally placed SBP1 outside the canonical PEXEL/Plasmepsin V export route.","evidence":"In vitro Plasmepsin V cleavage assays and N-terminal sequencing in P. falciparum showing no cleavage of the SBP1 N-terminus","pmids":["23387285"],"confidence":"Medium","gaps":["Alternative processing events not excluded","In vitro assay may not capture in-cell context"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2015,"claim":"Direct skeleton-binding assays and chaperone identification resolved the two ends of SBP1's dual role: cytoplasmic anchoring and chaperone-assisted lumenal export.","evidence":"Recombinant pulldowns with domain mapping in P. falciparum showing C-terminal binding to spectrin and protein 4.1R, and Co-IP showing N-terminal-dependent transport with the group II chaperonin PfTRiC","pmids":["25883090","25615740"],"confidence":"Medium","gaps":["Skeleton binding necessary but not sufficient for PfEMP1 translocation; N-terminal role uncharacterized","No in vitro reconstitution of the full complex","PfTRiC handoff to the clefts not resolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2016,"claim":"Cross-species genetics and immune-recognition studies established SBP1 as a conserved determinant of sequestration, virulence and surface antigen display.","evidence":"P. berghei KO/complementation with P. falciparum SBP1 and in vivo sequestration/virulence imaging; gene deletion with flow cytometry and opsonic phagocytosis in P. falciparum; localization of P. knowlesi SBP1 to cleft-analogous structures","pmids":["27225796","27193441","27732628"],"confidence":"High","gaps":["Molecular basis of conservation not defined","Which SBP1 domains drive cross-species rescue not mapped"],"attribution":[{"species":"Plasmodium berghei","strain":""},{"species":"Plasmodium falciparum","strain":""},{"species":"Plasmodium knowlesi","strain":""}]},{"year":2019,"claim":"Interactome and ultrastructural mapping enriched the export route with intermediate compartments and candidate partners.","evidence":"Affinity/proximity proteomics identifying exported and host partners including MAL8P1.4, and immuno-EM defining electron-dense material in the PV space as an export intermediate in P. falciparum","pmids":["31476617","31669509"],"confidence":"Medium","gaps":["Most interactome hits not individually validated","Functional role of the EDM intermediate not tested"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2023,"claim":"Time-resolved proximity labeling and topology assays refined the pre-export machinery and revealed a lumenal export intermediate for SBP1.","evidence":"SBP1-TurboID proximity biotinylation with conditional knockdown identifying essential plasma-membrane partners (one with a predicted translocon domain), and topology/ER-retention assays showing an ER-lumenal productive intermediate in P. falciparum","pmids":["37772444","37000891"],"confidence":"Medium","gaps":["Direct evidence that candidate translocon extracts SBP1 lacking","Mechanism converting lumenal intermediate to membrane-inserted cleft protein unknown"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2024,"claim":"Extending SBP1 to sexual stages showed its cleft residence and chaperone associations persist during gametocyte maturation.","evidence":"Immunofluorescence, Co-IP and mass spectrometry in P. falciparum gametocytes showing cleft localization and interaction with PfHSP70-1 and PfHSP70-x","pmids":["38331312"],"confidence":"Medium","gaps":["Functional consequence of HSP70 interactions in gametocytes untested","Role of SBP1 in transmission-stage biology unresolved"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"How the lumenal, chaperone-bound export intermediate is converted into a membrane-inserted, skeleton-anchored cleft protein — and precisely how SBP1 hands PfEMP1 to the erythrocyte surface — remains the central unresolved mechanism.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No reconstitution of the membrane-extraction/insertion step","Direct SBP1-PfEMP1 molecular contact not demonstrated","Structural model of SBP1 domains absent"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":["SBP1 C-terminal tail with erythrocyte spectrin and protein 4.1R (skeleton anchoring) [#9]","SBP1 C-terminal tail with host LANCL1 at Maurer's cleft surface [#4]","SBP1 N-terminal domain with group II chaperonin PfTRiC [#10]","SBP1 with PfHSP70-1 and PfHSP70-x in gametocytes [#21]","Tripartite in vitro complex of SBP1, PHISTc PFD1140w and PfEMP1 cytoplasmic tail [#16]","In vitro complex of SBP1, PfJ23 and PfEMP1 cytoplasmic tail [#17]"],"partners":["PFEMP1 (FUNCTIONAL DEPENDENCE FOR SURFACE TRANSLOCATION) [#1, #2]","SPECTRIN [#9]","PROTEIN 4.1R [#9]","LANCL1 (HOST) [#4]","PFTRIC GROUP II CHAPERONIN [#10]","PFBIP [#7]","PFHSP70-1 [#21]","PFHSP70-X [#21]","PROTEIN PHOSPHATASE 1 (PP1) [#3]","PHISTC PROTEINS PFD1140W AND PF11_0503 [#16]","PFJ23 (HYP16 FAMILY) [#17]","CBP2 CYTOPLASMIC DOMAIN [#18]","MAL8P1.4 [#14]","TWO PRE-EXPORT PLASMA-MEMBRANE PROTEINS, ONE WITH A PREDICTED TRANSLOCON DOMAIN [#19]"],"other_free_text":["SBP1 is exported by a PEXEL/Plasmepsin V-independent route; its transmembrane segment acts as an internal non-cleaved signal and its high-net-charge N-terminal region drives onward export [#5, #6, #8].","SBP1 transits an ER-lumenal topology and electron-dense material in the PV space as productive export intermediates before reaching Maurer's clefts [#20, #15].","SBP1 phosphorylation state at its N-terminal lumenal domain is controlled by a Maurer's cleft PP1-type phosphatase and links to host-cell rupture timing [#3].","SBP1 function is conserved across P. falciparum, P. berghei and P. knowlesi, with cross-species complementation restoring sequestration and virulence [#11, #13].","SBP1 governs the majority of antibody-accessible surface epitopes and opsonic phagocytosis of infected erythrocytes [#12]."]}},"prefetch_data":{},"corpus_meta":[{"pmid":"11087921","id":"PMC_11087921","title":"Pfsbp1, a Maurer's cleft Plasmodium falciparum protein, is associated with the erythrocyte skeleton.","date":"2000","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/11087921","citation_count":195,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["skeleton-binding protein 1","PfSBP1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"16520384","id":"PMC_16520384","title":"A Maurer's cleft-associated protein is essential for expression of the major malaria virulence antigen on the surface of infected red blood cells.","date":"2006","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/16520384","citation_count":152,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SBP1","skeleton-binding protein 1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"17023587","id":"PMC_17023587","title":"Skeleton-binding protein 1 functions at the parasitophorous vacuole membrane to traffic PfEMP1 to the Plasmodium falciparum-infected erythrocyte surface.","date":"2006","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/17023587","citation_count":137,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["skeleton-binding protein 1","PfSBP1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"23387285","id":"PMC_23387285","title":"Role of plasmepsin V in export of diverse protein families from the Plasmodium falciparum exportome.","date":"2013","source":"Traffic (Copenhagen, Denmark)","url":"https://pubmed.ncbi.nlm.nih.gov/23387285","citation_count":108,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SBP1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"19170882","id":"PMC_19170882","title":"Sequence requirements for the export of the Plasmodium falciparum Maurer's clefts protein REX2.","date":"2008","source":"Molecular 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profile of 3D7 after dihydroartemisinin treatment].","date":"2020","source":"Zhongguo Zhong yao za zhi = Zhongguo zhongyao zazhi = China journal of Chinese materia medica","url":"https://pubmed.ncbi.nlm.nih.gov/32495606","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["SBP1","PfSBP1"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":20924,"output_tokens":5900,"usd":0.075636,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12826,"output_tokens":5395,"usd":0.099502,"stage2_stop_reason":"end_turn"},"total_usd":0.175138,"stage1_batch_id":"msgbatch_01DbiymDmubkPpYvdbAu5a7V","stage2_batch_id":"msgbatch_012TbrWvMRH129T7PQ4SmvrJ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"SBP1 (PF3D7_0501300) is an integral membrane protein of Maurer's clefts. Its carboxy-terminal domain, exposed in the erythrocyte cytoplasm, interacts with a 35 kDa erythrocyte skeletal protein, suggesting SBP1 participates in anchoring Maurer's clefts to the erythrocyte submembrane skeleton.\",\n      \"method\": \"Immunoprecipitation with hyperimmune sera, subcellular fractionation, immunofluorescence/immunoelectron microscopy, domain analysis\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, Co-IP/fractionation showing C-terminal domain interaction with 35 kDa erythrocyte protein, replicated across two observations but no mutagenesis or reconstitution\",\n      \"pmids\": [\"11087921\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Targeted gene disruption of SBP1 in P. falciparum prevents PfEMP1 from reaching the infected red blood cell surface, abolishing IRBC adhesion. PfEMP1 remains in Maurer's clefts and other Maurer's cleft proteins are unaffected, but Maurer's clefts no longer localize close to the cell periphery. Complementation with sbp1 restores PfEMP1 surface expression and adhesion, demonstrating SBP1 is essential for PfEMP1 translocation to the IRBC surface.\",\n      \"method\": \"Targeted gene disruption, complementation, immunofluorescence microscopy, cytoadherence assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal genetic rescue (KO + complementation) with defined cellular phenotype, multiple orthogonal readouts (adhesion, surface expression, cleft localization)\",\n      \"pmids\": [\"16520384\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"SBP1 functions at the parasitophorous vacuole membrane to load PfEMP1 into Maurer's clefts during their formation. In the absence of SBP1, PfEMP1 fails to reach the IRBC surface and the dominant antibody response of malaria-exposed women to the IRBC surface is abolished.\",\n      \"method\": \"Gene disruption, live-cell imaging, immunofluorescence, antibody reactivity assays\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independent lab, gene disruption with defined mechanistic phenotype at the PVM, consistent with PMID:16520384\",\n      \"pmids\": [\"17023587\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Parasite protein phosphatase 1 (PP1) modulates the phosphorylation status of the amino-terminal domain of SBP1 within the lumen of Maurer's clefts, as shown by co-immunoprecipitation and inhibition studies. Hyperphosphorylation of SBP1 induced by a PP1 inhibitor (calyculin A) prevents merozoite release from the host cell, implicating PP1-mediated SBP1 phosphorylation in red blood cell rupture.\",\n      \"method\": \"Co-immunoprecipitation, pharmacological inhibition (calyculin A), phosphorylation assays\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, Co-IP plus pharmacological inhibition with functional phenotype, no direct mutagenesis of phosphosites\",\n      \"pmids\": [\"16548885\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The C-terminal cytoplasmic domain of SBP1 interacts with the human erythrocyte protein LANCL1, which is specifically recruited to the surface of Maurer's clefts in mature P. falciparum blood stages. This interaction was identified by co-immunoprecipitation and proposed to prevent premature rupture of the red blood cell.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence microscopy, mass spectrometry identification of LANCL1\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, Co-IP with MS identification plus localization, single method for functional inference\",\n      \"pmids\": [\"15811525\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The transmembrane domain of SBP1 functions as an internal signal sequence for entry into the parasite's secretory pathway and transport to the parasite plasma membrane. Additional N-terminal domains, characterized by high negative net charge, are required for trafficking beyond the parasite plasma membrane to the Maurer's clefts; these domains affect protein solubility, membrane orientation, and subcellular localization.\",\n      \"method\": \"Domain deletion/mutation analysis, biochemical fractionation, immunofluorescence microscopy, topology assays\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single lab, multiple domain constructs tested with biochemical and localization readouts, no in vitro reconstitution\",\n      \"pmids\": [\"19054387\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The N-terminal region and transmembrane domain of SBP1 can functionally replace the corresponding regions of the unrelated PEXEL-negative exported protein REX2 to direct export, demonstrating that these sequence features are shared among PEXEL-negative exported proteins and are sufficient for export when combined.\",\n      \"method\": \"Domain-swap chimera constructs, live-cell fluorescence microscopy, export assays\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single lab, domain-swap experiments with functional readout, but no mutagenesis of individual residues\",\n      \"pmids\": [\"19170882\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"During conditional export experiments, SBP1 physically interacts with the molecular chaperone PfBiP during early export steps, before reaching the Maurer's clefts.\",\n      \"method\": \"Conditional aggregation domain (CAD) export system, co-immunoprecipitation, immunofluorescence\",\n      \"journal\": \"Cellular microbiology\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single Co-IP in a conditional system; interaction inferred from the export system rather than direct biochemical reconstitution\",\n      \"pmids\": [\"18691247\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Plasmepsin V does not cleave the N-terminal sequence of SBP1, demonstrating that SBP1 is exported via a PEXEL/Plasmepsin V-independent pathway.\",\n      \"method\": \"In vitro Plasmepsin V cleavage assays, N-terminal sequencing\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic assay establishing a negative result (no cleavage), single lab; negative result is mechanistically informative\",\n      \"pmids\": [\"23387285\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The C-terminal cytoplasmic domain of SBP1 binds directly and specifically to defined sub-domains of two major RBC membrane skeleton components, protein 4.1R and spectrin. These interactions serve as a mechanism to anchor Maurer's clefts to the RBC membrane skeleton. However, these interactions alone are necessary but not sufficient for PfEMP1 translocation to the RBC surface; the N-terminal lumenal domain of SBP1 also plays an essential but uncharacterized role.\",\n      \"method\": \"Recombinant protein pulldown, binding domain mapping, complementary loss-of-function analysis\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, direct binding assays with domain mapping and functional inference from KO, but no in vitro reconstitution of full complex\",\n      \"pmids\": [\"25883090\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"SBP1 is exported to the Maurer's clefts as a soluble form in the red cell cytoplasm in association with the parasite group II chaperonin PfTRiC. The domain of interaction with PfTRiC resides within the amino-terminal domain of SBP1. This pathway appears to be shared among multiple Maurer's cleft membrane proteins with different export motifs.\",\n      \"method\": \"Co-immunoprecipitation, domain mapping, immunofluorescence microscopy\",\n      \"journal\": \"Traffic (Copenhagen, Denmark)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, Co-IP with domain mapping; interaction with PfTRiC shown biochemically but no in vitro reconstitution\",\n      \"pmids\": [\"25615740\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"P. berghei orthologues of SBP1 and MAHRP1 are required for CD36-mediated adhesion of P. berghei-infected RBCs to endothelium and for sequestration and virulence in mice. Complementation of P. berghei SBP1 KO with P. falciparum SBP1 restores sequestration and virulence, demonstrating functional conservation of SBP1 between rodent and human malaria parasites.\",\n      \"method\": \"Gene knockout, complementation with P. falciparum orthologue, bioluminescence imaging, in vivo adhesion/sequestration assays\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — cross-species complementation with KO and in vivo phenotypic rescue, multiple independent readouts\",\n      \"pmids\": [\"27225796\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Plasmodium berghei\", \"strain\": \"\"},\n        {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Genetic deletion of SBP1 leads to a dramatic reduction in antibody recognition of infected erythrocytes and in opsonic phagocytosis of IEs by human antibodies. The great majority of antibody epitopes on the IE surface are SBP1-dependent, establishing SBP1 as a critical component of the trafficking pathway for major surface antigens targeted by human immunity.\",\n      \"method\": \"Targeted gene deletion, flow cytometry, opsonic phagocytosis assays, multi-population antibody studies\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gene deletion with multiple orthogonal functional readouts across multiple parasite genetic backgrounds and human populations\",\n      \"pmids\": [\"27193441\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"P. knowlesi SBP1 (PkSBP1) localizes to membranous structures analogous to Maurer's clefts (Sinton and Mulligan stipplings) in both monkey and human erythrocytes infected with P. knowlesi. When expressed in P. falciparum-infected erythrocytes, recombinant PkSBP1 co-localizes with PfSBP1 at Maurer's clefts, indicating conserved trafficking.\",\n      \"method\": \"Epitope-tagged transgenic parasites, immunofluorescence assay, immunoelectron microscopy\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, direct localization experiment in two host cell types plus cross-species co-localization\",\n      \"pmids\": [\"27732628\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium knowlesi\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A comprehensive SBP1 interactome was mapped using sensitive proteomics approaches in P. falciparum-infected erythrocytes, identifying numerous exported parasite proteins and host-parasite interactions associated with SBP1 intracellular trafficking and virulence, including MAL8P1.4 as a linked virulence factor.\",\n      \"method\": \"Proximity-based/affinity proteomics (co-IP + mass spectrometry), functional validation of interactors\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single lab, MS-based interactome with functional follow-up on selected interactors, comprehensive but not individually reconstituted\",\n      \"pmids\": [\"31476617\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"At the early trophozoite (ring form) stage, SBP1 accumulates within electron-dense material (EDM) in the parasite cytoplasm and in the parasitophorous vacuolar space, before being transported to Maurer's clefts in the erythrocyte cytoplasm. This defines EDM as an intermediate compartment in SBP1's export pathway.\",\n      \"method\": \"Immunoelectron microscopy with specific anti-SBP1 antibodies\",\n      \"journal\": \"Parasitology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, direct ultrastructural localization at defined parasite stages; single method but specific spatial resolution\",\n      \"pmids\": [\"31669509\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Two PHISTc subfamily proteins (PFD1140w and PF11_0503) interact with SBP1 in vitro. PFD1140w interacts simultaneously with both PfEMP1 (cytoplasmic tail) and SBP1 to form a tripartite complex in vitro.\",\n      \"method\": \"Recombinant protein pulldown, co-immunoprecipitation, in vitro binding assay\",\n      \"journal\": \"The FEBS journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, in vitro binding assays with recombinant proteins; no in-cell validation of the SBP1-PHIST interaction\",\n      \"pmids\": [\"29155505\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"PfJ23, a PEXEL-positive hyp16 family member, directly interacts with purified SBP1 and both co-localize in parasites. PfEMP1 cytoplasmic tail, PfJ23, and SBP1 can form a complex in vitro, suggesting PfJ23 may assist in export of PEXEL-negative proteins including SBP1.\",\n      \"method\": \"Recombinant protein pulldown, in vitro co-immunoprecipitation, co-localization by immunofluorescence\",\n      \"journal\": \"Pathogens and disease\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, in vitro interaction only, limited functional validation\",\n      \"pmids\": [\"30576479\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The cytoplasmic domain of CBP2 (a 2TM exported protein) interacts in vitro with SBP1; this interaction is influenced by ATP binding of CBP2.\",\n      \"method\": \"In vitro recombinant protein binding assay\",\n      \"journal\": \"International journal of biological macromolecules\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single in vitro binding assay, no in-cell validation\",\n      \"pmids\": [\"31356937\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Using time-resolved proximity biotinylation (SBP1 fused to TurboID), two membrane-associated proteins were identified as pre-export (early) interactors of SBP1 at the parasite plasma membrane, one with a predicted translocon domain. Conditional knockdown of these candidates showed they are essential for asexual growth and localize to the host-parasite interface during early intraerythrocytic stages, suggesting a role in extracting membrane proteins from the parasite plasma membrane for export.\",\n      \"method\": \"TurboID proximity biotinylation, label-free quantitative proteomics, conditional knockdown, immunofluorescence\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single lab, time-resolved proximity proteomics plus conditional mutant phenotyping; novel mechanistic insight but pre-print-level validation of the translocon candidate\",\n      \"pmids\": [\"37772444\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SBP1 and MAHRP2, despite containing transmembrane segment-like hydrophobic sequences, assume a lumenal topology within the parasite secretory pathway (ER lumen) as a productive intermediate for protein export. Addition of a C-terminal ER-retention signal enhances but does not completely block retention of SBP1 in the parasite ER, indicating a sub-population adopts an ER-lumenal state during the export process.\",\n      \"method\": \"Epitope-tagged constructs, ER-retention signal fusion, immunofluorescence, biochemical topology assays in intact cells\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — single lab, multiple topology constructs with biochemical and imaging readouts; novel pathway finding but single lab\",\n      \"pmids\": [\"37000891\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"SBP1 localizes to dot-like Maurer's cleft structures in the cytoplasm of gametocyte-infected erythrocytes (not only asexual stages). Co-immunoprecipitation and mass spectrometry show that SBP1 interacts with the molecular chaperones PfHSP70-1 and PfHSP70-x during gametocyte maturation.\",\n      \"method\": \"Immunofluorescence microscopy, co-immunoprecipitation, mass spectrometry\",\n      \"journal\": \"Parasitology international\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — single lab, Co-IP with MS identification and localization in gametocytes; two orthogonal methods but single lab\",\n      \"pmids\": [\"38331312\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"SBP1 (PF3D7_0501300) is an integral Maurer's cleft membrane protein in P. falciparum that traffics through the parasite ER lumen and electron-dense material in the PV space before reaching erythrocyte-cytoplasmic Maurer's clefts; its transmembrane domain acts as an internal, non-cleaved signal for secretory pathway entry (independent of PEXEL/Plasmepsin V processing), while its N-terminal lumenal domain interacts with the chaperonin PfTRiC and HSP70s to facilitate export, and its C-terminal cytoplasmic domain anchors Maurer's clefts to the erythrocyte skeleton via direct binding to spectrin and protein 4.1R and to the host protein LANCL1; SBP1 is essential for the translocation of PfEMP1 from Maurer's clefts to the IRBC surface (functioning at the parasitophorous vacuole membrane during Maurer's cleft formation), and its phosphorylation state is regulated by a Maurer's cleft-resident PP1-type phosphatase, with this function conserved across Plasmodium species including P. berghei and P. knowlesi.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SBP1 (PF3D7_0501300) is an integral membrane protein of the Maurer's clefts in Plasmodium falciparum-infected erythrocytes that serves as a central component of the parasite's protein-export and cytoadherence machinery [#0, #1]. It is essential for translocation of the major virulence adhesin PfEMP1 from the Maurer's clefts to the infected-red-cell surface: gene disruption traps PfEMP1 in the clefts, abolishes IRBC adhesion, and mislocalizes the clefts away from the cell periphery, phenotypes reversed by complementation [#1], with SBP1 acting at the parasitophorous vacuole membrane to load PfEMP1 into forming clefts [#2]. Its transmembrane segment functions as an internal, non-cleaved signal directing entry into the secretory pathway independently of PEXEL/Plasmepsin V processing, while a high-net-charge N-terminal region is required for onward export to the clefts [#5, #8]. During export SBP1 transits an ER-lumenal state and electron-dense intermediate compartments in the parasitophorous vacuolar space before reaching the erythrocyte-cytoplasmic clefts [#20, #15], and its soluble transport is chaperone-assisted through the N-terminal domain via the group II chaperonin PfTRiC [#10]. At the clefts, the C-terminal cytoplasmic domain anchors the structures to the erythrocyte membrane skeleton through direct binding to spectrin and protein 4.1R [#9]. SBP1 function is conserved across Plasmodium: the P. berghei orthologue is required for CD36-mediated sequestration and virulence in vivo and is rescued by P. falciparum SBP1 [#11]. By controlling surface display of adhesins, SBP1 governs the great majority of antibody-accessible epitopes on the infected-cell surface and opsonic phagocytosis by human antibodies [#12].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing SBP1's physical identity and location answered where in the infected cell it acts and hinted at a structural anchoring role.\",\n      \"evidence\": \"Immunoprecipitation, fractionation and immuno-EM in P. falciparum showing an integral Maurer's cleft protein whose C-terminal domain binds a 35 kDa erythrocyte skeletal protein\",\n      \"pmids\": [\"11087921\"],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Identity of the 35 kDa partner not defined here\", \"No functional demonstration of anchoring\", \"No mutagenesis of the interacting domain\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identifying a host erythrocyte binding partner for the cytoplasmic tail extended SBP1's role to host-protein recruitment at the cleft surface.\",\n      \"evidence\": \"Co-IP with mass-spec identification and immunofluorescence in P. falciparum showing the C-terminal domain binds human LANCL1 recruited to Maurer's clefts\",\n      \"pmids\": [\"15811525\"],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Functional role in preventing rupture inferred, not demonstrated\", \"Single method for the functional claim\", \"Binding not mapped to residues\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Genetic ablation defined SBP1's essential cellular function — routing PfEMP1 to the IRBC surface — resolving whether SBP1 is structural or a trafficking determinant.\",\n      \"evidence\": \"Targeted disruption plus complementation with adhesion, surface-expression and cleft-localization readouts in P. falciparum; independent gene disruption localizing action to the PVM\",\n      \"pmids\": [\"16520384\", \"17023587\"],\n      \"confidence\": \"High\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Molecular mechanism of PfEMP1 loading at the PVM unresolved\", \"Direct PfEMP1-SBP1 contact not shown\", \"How SBP1 positions clefts at the periphery unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Linking SBP1 phosphorylation to a Maurer's cleft phosphatase connected its N-terminal state to the timing of host-cell rupture.\",\n      \"evidence\": \"Co-IP and calyculin A inhibition in P. falciparum showing PP1 modulates N-terminal SBP1 phosphorylation and that hyperphosphorylation blocks merozoite release\",\n      \"pmids\": [\"16548885\"],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Phosphosites not mapped by mutagenesis\", \"Direct causal link between SBP1 phosphorylation and rupture not isolated from PP1's other substrates\", \"Pharmacological rather than genetic evidence\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Dissecting the export signals showed how SBP1 enters and traverses the secretory pathway, defining transferable determinants of PEXEL-negative export.\",\n      \"evidence\": \"Domain deletion/topology assays and domain-swap chimeras with REX2, plus a conditional-export CAD system in P. falciparum identifying transmembrane and N-terminal export determinants and a PfBiP interaction\",\n      \"pmids\": [\"19054387\", \"19170882\", \"18691247\"],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Individual residue requirements not resolved\", \"PfBiP interaction rests on a single Co-IP in an artificial export system\", \"Mechanism of membrane extraction not addressed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"A negative enzymatic result formally placed SBP1 outside the canonical PEXEL/Plasmepsin V export route.\",\n      \"evidence\": \"In vitro Plasmepsin V cleavage assays and N-terminal sequencing in P. falciparum showing no cleavage of the SBP1 N-terminus\",\n      \"pmids\": [\"23387285\"],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Alternative processing events not excluded\", \"In vitro assay may not capture in-cell context\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Direct skeleton-binding assays and chaperone identification resolved the two ends of SBP1's dual role: cytoplasmic anchoring and chaperone-assisted lumenal export.\",\n      \"evidence\": \"Recombinant pulldowns with domain mapping in P. falciparum showing C-terminal binding to spectrin and protein 4.1R, and Co-IP showing N-terminal-dependent transport with the group II chaperonin PfTRiC\",\n      \"pmids\": [\"25883090\", \"25615740\"],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Skeleton binding necessary but not sufficient for PfEMP1 translocation; N-terminal role uncharacterized\", \"No in vitro reconstitution of the full complex\", \"PfTRiC handoff to the clefts not resolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Cross-species genetics and immune-recognition studies established SBP1 as a conserved determinant of sequestration, virulence and surface antigen display.\",\n      \"evidence\": \"P. berghei KO/complementation with P. falciparum SBP1 and in vivo sequestration/virulence imaging; gene deletion with flow cytometry and opsonic phagocytosis in P. falciparum; localization of P. knowlesi SBP1 to cleft-analogous structures\",\n      \"pmids\": [\"27225796\", \"27193441\", \"27732628\"],\n      \"confidence\": \"High\",\n      \"attribution\": [{\"species\": \"Plasmodium berghei\", \"strain\": \"\"}, {\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}, {\"species\": \"Plasmodium knowlesi\", \"strain\": \"\"}],\n      \"gaps\": [\"Molecular basis of conservation not defined\", \"Which SBP1 domains drive cross-species rescue not mapped\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Interactome and ultrastructural mapping enriched the export route with intermediate compartments and candidate partners.\",\n      \"evidence\": \"Affinity/proximity proteomics identifying exported and host partners including MAL8P1.4, and immuno-EM defining electron-dense material in the PV space as an export intermediate in P. falciparum\",\n      \"pmids\": [\"31476617\", \"31669509\"],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Most interactome hits not individually validated\", \"Functional role of the EDM intermediate not tested\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Time-resolved proximity labeling and topology assays refined the pre-export machinery and revealed a lumenal export intermediate for SBP1.\",\n      \"evidence\": \"SBP1-TurboID proximity biotinylation with conditional knockdown identifying essential plasma-membrane partners (one with a predicted translocon domain), and topology/ER-retention assays showing an ER-lumenal productive intermediate in P. falciparum\",\n      \"pmids\": [\"37772444\", \"37000891\"],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Direct evidence that candidate translocon extracts SBP1 lacking\", \"Mechanism converting lumenal intermediate to membrane-inserted cleft protein unknown\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extending SBP1 to sexual stages showed its cleft residence and chaperone associations persist during gametocyte maturation.\",\n      \"evidence\": \"Immunofluorescence, Co-IP and mass spectrometry in P. falciparum gametocytes showing cleft localization and interaction with PfHSP70-1 and PfHSP70-x\",\n      \"pmids\": [\"38331312\"],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"Functional consequence of HSP70 interactions in gametocytes untested\", \"Role of SBP1 in transmission-stage biology unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the lumenal, chaperone-bound export intermediate is converted into a membrane-inserted, skeleton-anchored cleft protein — and precisely how SBP1 hands PfEMP1 to the erythrocyte surface — remains the central unresolved mechanism.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}],\n      \"gaps\": [\"No reconstitution of the membrane-extraction/insertion step\", \"Direct SBP1-PfEMP1 molecular contact not demonstrated\", \"Structural model of SBP1 domains absent\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 9]},\n      {\"term_id\": \"GO:0005543\", \"supporting_discovery_ids\": [9]},\n      {\"term_id\": \"GO:0051082\", \"supporting_discovery_ids\": [10, 7, 21]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0020030\", \"supporting_discovery_ids\": [0, 1, 13, 15, 21]},\n      {\"term_id\": \"GO:0016020\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [20]},\n      {\"term_id\": \"GO:0020005\", \"supporting_discovery_ids\": [15]},\n      {\"term_id\": \"GO:0020002\", \"supporting_discovery_ids\": [2, 19]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0046903\", \"supporting_discovery_ids\": [5, 6, 8, 20]},\n      {\"term_id\": \"GO:0006612\", \"supporting_discovery_ids\": [5, 20]},\n      {\"term_id\": \"GO:0007155\", \"supporting_discovery_ids\": [1, 11]},\n      {\"term_id\": \"GO:0051701\", \"supporting_discovery_ids\": [12]}\n    ],\n    \"complexes\": [\n      \"SBP1 C-terminal tail with erythrocyte spectrin and protein 4.1R (skeleton anchoring) [#9]\",\n      \"SBP1 C-terminal tail with host LANCL1 at Maurer's cleft surface [#4]\",\n      \"SBP1 N-terminal domain with group II chaperonin PfTRiC [#10]\",\n      \"SBP1 with PfHSP70-1 and PfHSP70-x in gametocytes [#21]\",\n      \"Tripartite in vitro complex of SBP1, PHISTc PFD1140w and PfEMP1 cytoplasmic tail [#16]\",\n      \"In vitro complex of SBP1, PfJ23 and PfEMP1 cytoplasmic tail [#17]\"\n    ],\n    \"partners\": [\n      \"PfEMP1 (functional dependence for surface translocation) [#1, #2]\",\n      \"Spectrin [#9]\",\n      \"Protein 4.1R [#9]\",\n      \"LANCL1 (host) [#4]\",\n      \"PfTRiC group II chaperonin [#10]\",\n      \"PfBiP [#7]\",\n      \"PfHSP70-1 [#21]\",\n      \"PfHSP70-x [#21]\",\n      \"Protein phosphatase 1 (PP1) [#3]\",\n      \"PHISTc proteins PFD1140w and PF11_0503 [#16]\",\n      \"PfJ23 (hyp16 family) [#17]\",\n      \"CBP2 cytoplasmic domain [#18]\",\n      \"MAL8P1.4 [#14]\",\n      \"Two pre-export plasma-membrane proteins, one with a predicted translocon domain [#19]\"\n    ],\n    \"other_free_text\": [\n      \"SBP1 is exported by a PEXEL/Plasmepsin V-independent route; its transmembrane segment acts as an internal non-cleaved signal and its high-net-charge N-terminal region drives onward export [#5, #6, #8].\",\n      \"SBP1 transits an ER-lumenal topology and electron-dense material in the PV space as productive export intermediates before reaching Maurer's clefts [#20, #15].\",\n      \"SBP1 phosphorylation state at its N-terminal lumenal domain is controlled by a Maurer's cleft PP1-type phosphatase and links to host-cell rupture timing [#3].\",\n      \"SBP1 function is conserved across P. falciparum, P. berghei and P. knowlesi, with cross-species complementation restoring sequestration and virulence [#11, #13].\",\n      \"SBP1 governs the majority of antibody-accessible surface epitopes and opsonic phagocytosis of infected erythrocytes [#12].\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_0501300","name":null,"product":"skeleton-binding protein 1","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_1032400","name":null,"product":"skeleton-binding protein 1","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"SBP1","evaluation":null}