Affinage · Plasmodium

P28

PF3D7_1030900 · ookinete surface protein P28

Annotated
2026-09-08
19 papers in source corpus 8 papers cited in narrative 8 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

P28 (PF3D7_1030900) is a GPI-anchored surface protein of the Plasmodium ookinete that acts, together with its genetically linked paralog P25, to protect the developing parasite during passage through the mosquito midgut and to enable its transformation into an oocyst (PMID:11483501, PMID:9038325). In P. berghei, single loss of P28 only mildly compromises ookinete/oocyst development, but simultaneous knock-out of both P25 and P28 severely impairs protection against midgut proteases and other lethal factors, traversal of the midgut epithelium, and oocyst formation, defining the two proteins as partially redundant (PMID:11483501). The double knock-out also fails to elicit the SRPN10 serpin redistribution and apoptotic 'time bomb' response that invaded midgut cells mount against wild-type ookinetes, placing P28/P25 upstream of this host invasion response (PMID:15659062). At the molecular level, P28 (Pbs21) is tethered to the plasma membrane by a C-terminal GPI anchor signal whose 25 residues are required for surface localization and full immunogenicity (PMID:11012975), and P28 of P. berghei binds Anopheles laminin gamma 1 directly, more weakly than P25 does (PMID:11223130). Structurally, the P25/P28 family adopts a triangular-prism fold of four EGF-like domains with a conserved interface (PMID:16327807). In P. falciparum, antibodies to P28 block transmission and act synergistically with anti-P25 antibodies (PMID:9038325).

Mechanistic history

Synthesis pass · year-by-year structured walk · 7 steps
  1. 1997 Medium

    Establishing whether P28 was an independent transmission-blocking target answered whether it warranted vaccine development alongside its linked paralog P25.

    Evidence Genetic linkage mapping on P. falciparum chromosome 10 plus antibody transmission-blocking (membrane feeding) assays

    PMID:9038325

    Open questions at the time
    • Did not resolve the endogenous cellular function of P28
    • Synergy mechanism between anti-P28 and anti-P25 antibodies not defined
    • Single-lab characterization
  2. 2000 Medium

    Mapping the membrane-attachment determinant showed how P28 is displayed on the ookinete surface, a prerequisite for both its function and antibody accessibility.

    Evidence Baculovirus expression of full-length and C-terminal deletion constructs with surface detection in Sf21 cells and immunization readout

    PMID:11012975

    Open questions at the time
    • GPI anchoring shown in insect cells, not directly in the parasite
    • Does not address the protein's molecular partners
  3. 2001 High

    Loss-of-function genetics resolved whether P28 has a distinct role or is redundant with P25 during mosquito-stage development.

    Evidence Single and double gene knock-outs in P. berghei with phenotypic analysis of protease protection, epithelium traversal and oocyst formation

    PMID:11483501

    Open questions at the time
    • Does not define the biochemical basis of protease protection
    • Molecular mechanism of epithelium traversal not resolved
    • Relative contribution of P28 versus P25 not quantified at the molecular level
  4. 2001 Medium

    Identifying a mosquito binding partner addressed how P28 engages the host midgut, providing a candidate molecular basis for epithelium interaction.

    Evidence Yeast two-hybrid and in vitro pull-down of purified P28 and Anopheles gambiae laminin gamma 1 fusion proteins

    PMID:11223130

    Open questions at the time
    • Weaker binding than P25 leaves the in vivo relevance for P28 uncertain
    • No structural mapping of the binding interface
    • Not validated in vivo
  5. 2005 High

    Determining the family fold established the structural architecture underlying P28 function and antibody recognition.

    Evidence X-ray crystallography of Pvs25 alone and co-crystallized with a transmission-blocking antibody, plus cross-species conservation analysis

    PMID:16327807

    Open questions at the time
    • Structure solved for the P25-family member Pvs25, not for P28 directly
    • P28-specific structural features not experimentally resolved
  6. 2005 Medium

    Linking P28/P25 to the host apoptotic invasion response placed the proteins upstream of the midgut 'time bomb' defense.

    Evidence SRPN10 localization and expression analysis in midgut cells invaded by wild-type versus P25/P28 double knock-out P. berghei ookinetes

    PMID:15659062

    Open questions at the time
    • Cannot separate the individual contribution of P28 from P25
    • Mechanism linking surface proteins to SRPN10 redistribution unknown
  7. 2008 Low

    Computational modelling attempted to localize the antibody epitope and define P28-family-specific structural features in the absence of an experimental P28 structure.

    Evidence Homology modelling and ZDOCK/RDOCK docking of P. berghei Pb28 and comparative modelling across six P28 family members

    PMID:19057932 PMID:19066995

    Open questions at the time
    • Computational prediction only, no experimental structural validation
    • Docked epitope on EGF domain II not confirmed by mutagenesis or crystallography
    • The proposed EGF-IV large C-loop hallmark of the P28 family lacks experimental structure

Open questions

Synthesis pass · forward-looking unresolved questions
  • The biochemical mechanism by which P28 protects ookinetes from proteases and enables epithelium traversal, and its non-redundant contribution independent of P25, remain undefined.
  • No experimental structure of P28 itself
  • No mechanistic account of protease resistance
  • P28-specific (versus P25-shared) functional contribution not isolated

Mechanism profile

Synthesis pass · controlled-vocabulary classification
Partners
ANOPHELES GAMBIAE LAMININ GAMMA 1 [#2]P25 (PARALOG, FUNCTIONALLY REDUNDANT) [#0]

Evidence

Reading pass · 8 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2001 P28 (and P25) have multiple partially redundant functions during ookinete/oocyst development in the mosquito midgut: they protect ookinetes against lethal factors including protease attack, and are required for efficient traversal of the midgut epithelium and transformation into oocysts. Single knock-out of P28 alone only mildly compromises development, but double knock-out of both P25 and P28 severely impairs all these steps. Single and double gene knock-out in Plasmodium berghei; phenotypic analysis of ookinete/oocyst development in mosquito midgut The EMBO journal High 11483501
1997 P28 (Pfs28) and P25 (Pfs25) are structurally similar, genetically linked on chromosome 10 of P. falciparum, and antibodies to Pfs28 block P. falciparum transmission; combining anti-Pfs28 and anti-Pfs25 antibodies produces synergistic transmission-blocking activity. Genetic linkage mapping; antibody-based transmission-blocking assays (membrane feeding assay) Infection and immunity Medium 9038325
2001 Anopheles gambiae laminin gamma 1 interacts with P28 of Plasmodium berghei, albeit more weakly than with P25, as demonstrated by yeast two-hybrid and in vitro binding of purified fusion proteins. This interaction does not require additional protein factors. Yeast two-hybrid system; in vitro pull-down with purified fusion proteins Molecular and biochemical parasitology Medium 11223130
2005 The P25 and P28 proteins adopt a triangular prism structure composed of four EGF-like domains; the residues forming the triangular prism interface are conserved across P25 and P28 from all Plasmodium species, suggesting a conserved tile-like surface assembly. A co-crystal of Pvs25 with a transmission-blocking antibody shows the antibody heavy chain binds at a vertex of the triangle. X-ray crystallography (crystal structure of Pvs25; co-crystal with transmission-blocking antibody); sequence conservation analysis Nature structural & molecular biology High 16327807
2000 The GPI anchor signal encoded by the 25 C-terminal amino acids of P28 (Pbs21) from P. berghei is critical for attachment of the protein to the plasma membrane; deletion of these residues abolishes cell-surface localization in insect cells and reduces immunogenicity of the recombinant protein. Baculovirus expression of full-length and C-terminal deletion constructs; subcellular fractionation; cell-surface detection in Sf21 cells; immunization and transmission-blocking assay in mice Parasite immunology Medium 11012975
2005 Ookinetes lacking both P25 and P28 (double knock-out) fail to elicit the SRPN10 serpin redistribution and apoptotic response in invaded midgut epithelial cells that wild-type ookinetes provoke, indicating P28 and P25 together are required for triggering the host cell 'time bomb' invasion response. Analysis of SRPN10 localization and expression in mosquito midgut cells invaded by wild-type vs. P25/P28 double knock-out P. berghei ookinetes; immunofluorescence; quantitative analysis Cellular microbiology Medium 15659062
2008 Computational modelling of Pb28 from P. berghei predicts four EGF-like domains arranged in a triangular form, and molecular docking suggests that the B loop of EGF domain II of Pb28 interacts with the scFv of transmission-blocking monoclonal antibody 13.1. Homology modelling; ZDOCK/RDOCK molecular docking Journal of molecular modeling Low 19066995
2008 Homology modelling of six P28 family members reveals that all possess four EGF-like domains in a triangular arrangement, with a distinctive very large C-loop in EGF domain IV that is absent in P25 family members, constituting a structural hallmark of the P28 family. Homology modelling; comparative sequence/structural analysis Journal of molecular modeling Low 19057932

Source papers

Stage 0 corpus · 19 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2001 P25 and P28 proteins of the malaria ookinete surface have multiple and partially redundant functions. The EMBO journal 176 11483501
1997 A novel malaria protein, Pfs28, and Pfs25 are genetically linked and synergistic as falciparum malaria transmission-blocking vaccines. Infection and immunity 146 9038325
2014 Experimental study of the relationship between Plasmodium gametocyte density and infection success in mosquitoes; implications for the evaluation of malaria transmission-reducing interventions. Experimental parasitology 63 25541384
2007 Mosquito stage, transmission blocking vaccines for malaria. Current opinion in infectious diseases 63 17762780
2005 The essential mosquito-stage P25 and P28 proteins from Plasmodium form tile-like triangular prisms. Nature structural & molecular biology 58 16327807
2001 Anopheles gambiae laminin interacts with the P25 surface protein of Plasmodium berghei ookinetes. Molecular and biochemical parasitology 56 11223130
2006 The use of transgenic Plasmodium berghei expressing the Plasmodium vivax antigen P25 to determine the transmission-blocking activity of sera from malaria vaccine trials. Vaccine 47 17049690
2010 Intranasal and intramuscular immunization with Baculovirus Dual Expression System-based Pvs25 vaccine substantially blocks Plasmodium vivax transmission. Vaccine 46 20637303
2001 Cryofracture electron microscopy of the ookinete pellicle of Plasmodium gallinaceum reveals the existence of novel pores in the alveolar membranes. Journal of structural biology 45 11562165
2005 Overexpression and altered nucleocytoplasmic distribution of Anopheles ovalbumin-like SRPN10 serpins in Plasmodium-infected midgut cells. Cellular microbiology 44 15659062
2016 CRISPR/Cas9 mediated sequential editing of genes critical for ookinete motility in Plasmodium yoelii. Molecular and biochemical parasitology 41 28034675
2007 Plasmodium p25 and p28 surface proteins: potential transmission-blocking vaccines. Eukaryotic cell 37 17557884
2005 Do malaria ookinete surface proteins P25 and P28 mediate parasite entry into mosquito midgut epithelial cells? Malaria journal 34 15733320
2007 The surface protein Pvs25 of Plasmodium vivax ookinetes interacts with calreticulin on the midgut apical surface of the malaria vector Anopheles albimanus. Molecular and biochemical parasitology 24 17442413
2006 3' gene regulatory elements required for expression of the Plasmodiumfalciparum developmental protein, Pfs25. Molecular and biochemical parasitology 18 16439031
2008 Structure and mechanism of a transmission blocking vaccine candidate protein Pfs25 from P. falciparum: a molecular modeling and docking study. In silico biology 10 19032156
2000 The roles of the glycosylphosphatidylinositol anchor on the production and immunogenicity of recombinant ookinete surface antigen Pbs21 of Plasmodium berghei when prepared in a baculovirus expression system. Parasite immunology 8 11012975
2008 EGF domain II of protein Pb28 from Plasmodium berghei interacts with monoclonal transmission blocking antibody 13.1. Journal of molecular modeling 6 19066995
2008 A very large C-loop in EGF domain IV is characteristic of the P28 family of ookinete surface proteins. Journal of molecular modeling 3 19057932