Affinage · Plasmodium

SBP1

PF3D7_0501300 · skeleton-binding protein 1

Annotated
2026-09-07
36 papers in source corpus 22 papers cited in narrative 22 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

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).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 2000 Medium

    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

    PMID:11087921

    Open questions at the time
    • Identity of the 35 kDa partner not defined here
    • No functional demonstration of anchoring
    • No mutagenesis of the interacting domain
  2. 2005 Medium

    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

    PMID:15811525

    Open questions at the time
    • Functional role in preventing rupture inferred, not demonstrated
    • Single method for the functional claim
    • Binding not mapped to residues
  3. 2006 High

    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

    PMID:16520384 PMID:17023587

    Open questions at the time
    • Molecular mechanism of PfEMP1 loading at the PVM unresolved
    • Direct PfEMP1-SBP1 contact not shown
    • How SBP1 positions clefts at the periphery unknown
  4. 2006 Medium

    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

    PMID:16548885

    Open questions at the time
    • 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
  5. 2008 Medium

    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

    PMID:18691247 PMID:19054387 PMID:19170882

    Open questions at the time
    • Individual residue requirements not resolved
    • PfBiP interaction rests on a single Co-IP in an artificial export system
    • Mechanism of membrane extraction not addressed
  6. 2013 Medium

    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

    PMID:23387285

    Open questions at the time
    • Alternative processing events not excluded
    • In vitro assay may not capture in-cell context
  7. 2015 Medium

    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

    PMID:25615740 PMID:25883090

    Open questions at the time
    • 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
  8. 2016 High

    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

    PMID:27193441 PMID:27225796 PMID:27732628

    Open questions at the time
    • Molecular basis of conservation not defined
    • Which SBP1 domains drive cross-species rescue not mapped
  9. 2019 Medium

    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

    PMID:31476617 PMID:31669509

    Open questions at the time
    • Most interactome hits not individually validated
    • Functional role of the EDM intermediate not tested
  10. 2023 Medium

    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

    PMID:37000891 PMID:37772444

    Open questions at the time
    • Direct evidence that candidate translocon extracts SBP1 lacking
    • Mechanism converting lumenal intermediate to membrane-inserted cleft protein unknown
  11. 2024 Medium

    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

    PMID:38331312

    Open questions at the time
    • Functional consequence of HSP70 interactions in gametocytes untested
    • Role of SBP1 in transmission-stage biology unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • 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.
  • No reconstitution of the membrane-extraction/insertion step
  • Direct SBP1-PfEMP1 molecular contact not demonstrated
  • Structural model of SBP1 domains absent

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Complex memberships
In vitro complex of SBP1, PfJ23 and PfEMP1 cytoplasmic tail [#17]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]

Evidence

Reading pass · 22 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2000 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. Immunoprecipitation with hyperimmune sera, subcellular fractionation, immunofluorescence/immunoelectron microscopy, domain analysis Molecular and biochemical parasitology Medium 11087921
2006 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. Targeted gene disruption, complementation, immunofluorescence microscopy, cytoadherence assays The Journal of cell biology High 16520384
2006 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. Gene disruption, live-cell imaging, immunofluorescence, antibody reactivity assays Blood High 17023587
2006 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. Co-immunoprecipitation, pharmacological inhibition (calyculin A), phosphorylation assays Cellular microbiology Medium 16548885
2005 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. Co-immunoprecipitation, immunofluorescence microscopy, mass spectrometry identification of LANCL1 Molecular and biochemical parasitology Medium 15811525
2008 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. Domain deletion/mutation analysis, biochemical fractionation, immunofluorescence microscopy, topology assays Traffic (Copenhagen, Denmark) Medium 19054387
2008 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. Domain-swap chimera constructs, live-cell fluorescence microscopy, export assays Molecular microbiology Medium 19170882
2008 During conditional export experiments, SBP1 physically interacts with the molecular chaperone PfBiP during early export steps, before reaching the Maurer's clefts. Conditional aggregation domain (CAD) export system, co-immunoprecipitation, immunofluorescence Cellular microbiology Low 18691247
2013 Plasmepsin V does not cleave the N-terminal sequence of SBP1, demonstrating that SBP1 is exported via a PEXEL/Plasmepsin V-independent pathway. In vitro Plasmepsin V cleavage assays, N-terminal sequencing Traffic (Copenhagen, Denmark) Medium 23387285
2015 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. Recombinant protein pulldown, binding domain mapping, complementary loss-of-function analysis Biochimica et biophysica acta Medium 25883090
2015 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. Co-immunoprecipitation, domain mapping, immunofluorescence microscopy Traffic (Copenhagen, Denmark) Medium 25615740
2016 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. Gene knockout, complementation with P. falciparum orthologue, bioluminescence imaging, in vivo adhesion/sequestration assays Nature communications High 27225796
2016 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. Targeted gene deletion, flow cytometry, opsonic phagocytosis assays, multi-population antibody studies Cellular and molecular life sciences : CMLS High 27193441
2016 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. Epitope-tagged transgenic parasites, immunofluorescence assay, immunoelectron microscopy PloS one Medium 27732628
2019 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. Proximity-based/affinity proteomics (co-IP + mass spectrometry), functional validation of interactors iScience Medium 31476617
2019 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. Immunoelectron microscopy with specific anti-SBP1 antibodies Parasitology international Medium 31669509
2017 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. Recombinant protein pulldown, co-immunoprecipitation, in vitro binding assay The FEBS journal Low 29155505
2018 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. Recombinant protein pulldown, in vitro co-immunoprecipitation, co-localization by immunofluorescence Pathogens and disease Low 30576479
2019 The cytoplasmic domain of CBP2 (a 2TM exported protein) interacts in vitro with SBP1; this interaction is influenced by ATP binding of CBP2. In vitro recombinant protein binding assay International journal of biological macromolecules Low 31356937
2023 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. TurboID proximity biotinylation, label-free quantitative proteomics, conditional knockdown, immunofluorescence Journal of cell science Medium 37772444
2023 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. Epitope-tagged constructs, ER-retention signal fusion, immunofluorescence, biochemical topology assays in intact cells PLoS pathogens Medium 37000891
2024 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. Immunofluorescence microscopy, co-immunoprecipitation, mass spectrometry Parasitology international Medium 38331312

Source papers

Stage 0 corpus · 36 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2000 Pfsbp1, a Maurer's cleft Plasmodium falciparum protein, is associated with the erythrocyte skeleton. Molecular and biochemical parasitology 195 11087921
2006 A Maurer's cleft-associated protein is essential for expression of the major malaria virulence antigen on the surface of infected red blood cells. The Journal of cell biology 152 16520384
2006 Skeleton-binding protein 1 functions at the parasitophorous vacuole membrane to traffic PfEMP1 to the Plasmodium falciparum-infected erythrocyte surface. Blood 137 17023587
2013 Role of plasmepsin V in export of diverse protein families from the Plasmodium falciparum exportome. Traffic (Copenhagen, Denmark) 108 23387285
2008 Sequence requirements for the export of the Plasmodium falciparum Maurer's clefts protein REX2. Molecular microbiology 71 19170882
2016 The machinery underlying malaria parasite virulence is conserved between rodent and human malaria parasites. Nature communications 60 27225796
2008 Export of PfSBP1 to the Plasmodium falciparum Maurer's clefts. Traffic (Copenhagen, Denmark) 59 19054387
2006 Protein phosphatase 1, a Plasmodium falciparum essential enzyme, is exported to the host cell and implicated in the release of infectious merozoites. Cellular microbiology 40 16548885
2005 LANCL1, an erythrocyte protein recruited to the Maurer's clefts during Plasmodium falciparum development. Molecular and biochemical parasitology 34 15811525
2015 Interactions between Plasmodium falciparum skeleton-binding protein 1 and the membrane skeleton of malaria-infected red blood cells. Biochimica et biophysica acta 26 25883090
2008 A conditional export system provides new insights into protein export in Plasmodium falciparum-infected erythrocytes. Cellular microbiology 26 18691247
2017 Molecular Markers for Sensitive Detection of Plasmodium falciparum Asexual Stage Parasites and their Application in a Malaria Clinical Trial. The American journal of tropical medicine and hygiene 24 28719294
2011 Amplification of P. falciparum Cytoadherence through induction of a pro-adhesive state in host endothelium. PloS one 22 22043276
2016 A single point in protein trafficking by Plasmodium falciparum determines the expression of major antigens on the surface of infected erythrocytes targeted by human antibodies. Cellular and molecular life sciences : CMLS 20 27193441
2016 Plasmodium knowlesi Skeleton-Binding Protein 1 Localizes to the 'Sinton and Mulligan' Stipplings in the Cytoplasm of Monkey and Human Erythrocytes. PloS one 16 27732628
2017 PHISTc protein family members localize to different subcellular organelles and bind Plasmodium falciparum major virulence factor PfEMP-1. The FEBS journal 15 29155505
2015 New Export Pathway in Plasmodium falciparum-Infected Erythrocytes: Role of the Parasite Group II Chaperonin, PfTRiC. Traffic (Copenhagen, Denmark) 15 25615740
2010 Functional evaluation of Plasmodium export signals in Plasmodium berghei suggests multiple modes of protein export. PloS one 15 20419102
2019 Plasmodium falciparum Gametocyte Enrichment in Peripheral Blood Samples by Magnetic Fractionation: Gametocyte Yields and Possibilities to Reuse Columns. The American journal of tropical medicine and hygiene 13 30608048
2023 Time-resolved proximity biotinylation implicates a porin protein in export of transmembrane malaria parasite effectors. Journal of cell science 11 37772444
2022 Experimental malaria-associated acute kidney injury is independent of parasite sequestration and resolves upon antimalarial treatment. Frontiers in cellular and infection microbiology 11 36004329
2021 Skeleton binding protein-1-mediated parasite sequestration inhibits spontaneous resolution of malaria-associated acute respiratory distress syndrome. PLoS pathogens 11 34843584
2019 A High-Resolution Map of SBP1 Interactomes in Plasmodium falciparum-infected Erythrocytes. iScience 11 31476617
2018 Comparative genomics and proteomic analyses between lethal and nonlethal strains of Plasmodium berghei. Experimental parasitology 8 29307564
2017 A Direct from Blood Reverse Transcriptase Polymerase Chain Reaction Assay for Monitoring Falciparum Malaria Parasite Transmission in Elimination Settings. The American journal of tropical medicine and hygiene 8 28722583
2024 Persistent and multiclonal malaria parasite dynamics despite extended artemether-lumefantrine treatment in children. Nature communications 7 38714692
2019 Skeleton binding protein 1 (SBP1) of Plasmodium falciparum accumulates in electron-dense material before passing through the parasitophorous vacuole membrane. Parasitology international 7 31669509
2006 Deciphering the export pathway of malaria surface proteins. Trends in parasitology 7 16843728
2025 Isolation and characterization of Plasmodium falciparum blood-stage persisters by improved selection protocols using dihydroartemisinin alone. Antimicrobial agents and chemotherapy 5 39927767
2021 Persistence of mRNA indicative of Plasmodium falciparum ring-stage parasites 42 days after artemisinin and non-artemisinin combination therapy in naturally infected Malians. Malaria journal 5 33422068
2023 Formation of ER-lumenal intermediates during export of Plasmodium proteins containing transmembrane-like hydrophobic sequences. PLoS pathogens 4 37000891
2018 Plasmodium falciparum protein 'PfJ23' hosts distinct binding sites for major virulence factor 'PfEMP1' and Maurer's cleft marker 'PfSBP1'. Pathogens and disease 3 30576479
2024 Transcriptional responses of brain endothelium to Plasmodium falciparum patient-derived isolates in vitro. Microbiology spectrum 1 38864616
2019 CX3CL1 binding protein-2 (CBP2) of Plasmodium falciparum binds nucleic acids. International journal of biological macromolecules 1 31356937
2024 Skeleton binding protein 1 localizes to the Maurer's cleft and interacts with PfHSP70-1 and PfHSP70-x in Plasmodium falciparum gametocyte-infected erythrocytes. Parasitology international 0 38331312
2020 [Method for rapid synchronization of different growth cycles of Plasmodium falciparum in vitro and application in differential gene expression profile of 3D7 after dihydroartemisinin treatment]. Zhongguo Zhong yao za zhi = Zhongguo zhongyao zazhi = China journal of Chinese materia medica 0 32495606