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Crystal structure of Plasmodium knowlesi apical membrane antigen 1 and its complex with an invasion-inhibitory monoclonal antibody.

Vulliez-Le Normand B, Faber BW, Saul FA, van der Eijk M, Thomas AW, Singh B, Kocken CH, Bentley GA - PLoS ONE (2015)

Bottom Line: R31C2 inhibits binding of the Rhoptry Neck Protein 2 (RON2) receptor by steric blocking of the hydrophobic groove and by preventing the displacement of the D2 loop which is essential for exposing the complete binding site on AMA1.PkAMA1 is much less polymorphic than the P. falciparum and P. vivax orthologues.Unlike these two latter species, there are no polymorphic sites close to the RON2-binding site of PkAMA1, suggesting that P. knowlesi has not developed a mechanism of immune escape from the host's humoral response to AMA1.

View Article: PubMed Central - PubMed

Affiliation: Institut Pasteur, Unité d'Immunologie Structurale, Département de Biologie Structurale et Chimie, Paris, France; CNRS URA 2185, Paris, France.

ABSTRACT
The malaria parasite Plasmodium knowlesi, previously associated only with infection of macaques, is now known to infect humans as well and has become a significant public health problem in Southeast Asia. This species should therefore be targeted in vaccine and therapeutic strategies against human malaria. Apical Membrane Antigen 1 (AMA1), which plays a role in Plasmodium merozoite invasion of the erythrocyte, is currently being pursued in human vaccine trials against P. falciparum. Recent vaccine trials in macaques using the P. knowlesi orthologue PkAMA1 have shown that it protects against infection by this parasite species and thus should be developed for human vaccination as well. Here, we present the crystal structure of Domains 1 and 2 of the PkAMA1 ectodomain, and of its complex with the invasion-inhibitory monoclonal antibody R31C2. The Domain 2 (D2) loop, which is displaced upon binding the Rhoptry Neck Protein 2 (RON2) receptor, makes significant contacts with the antibody. R31C2 inhibits binding of the Rhoptry Neck Protein 2 (RON2) receptor by steric blocking of the hydrophobic groove and by preventing the displacement of the D2 loop which is essential for exposing the complete binding site on AMA1. R31C2 recognizes a non-polymorphic epitope and should thus be cross-strain reactive. PkAMA1 is much less polymorphic than the P. falciparum and P. vivax orthologues. Unlike these two latter species, there are no polymorphic sites close to the RON2-binding site of PkAMA1, suggesting that P. knowlesi has not developed a mechanism of immune escape from the host's humoral response to AMA1.

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Structure of domains 1 and 2 of PkAMA1 in the non-complexed form.The structure of PkAMA1 (molecule B) is shown in ribbon representation with Domain 1 in green and Domain 2 in light brown. The Domain 2 loop is shown in red and the c-myc tail is shown in mauve. The N- and C-termini are indicated by N and C, respectively. A gap occurs within the D2 loop since the protein could not be traced from residues Gly328 to Ser332.
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pone.0123567.g001: Structure of domains 1 and 2 of PkAMA1 in the non-complexed form.The structure of PkAMA1 (molecule B) is shown in ribbon representation with Domain 1 in green and Domain 2 in light brown. The Domain 2 loop is shown in red and the c-myc tail is shown in mauve. The N- and C-termini are indicated by N and C, respectively. A gap occurs within the D2 loop since the protein could not be traced from residues Gly328 to Ser332.

Mentions: The free PkAMA1 protein crystallized in space group C2 with two molecules (A and B) in the asymmetric unit and the structure was refined at 2.45 Å resolution (Table 1, Table 2). The polypeptide chain of molecule A was traced from Ser52 to Glu397 (thus including eight residues of the c-myc tag), with main-chain gaps Ala131-Asp132, Ser212-Lys215 and Gly328-Asn331 due to conformational mobility. Molecule B (Fig 1) was built from Ser52 to Asp398 with main-chain gaps Ser212-Ala217 and Gly328-Ser332. The two molecules are very similar, with an r.m.s.d. of 0.34 Å in Cα positions over the 332 common residues in the PkAMA1 sequence. The D2 loop of PkAMA1, which is displaced upon binding of the RON2 component of the RON receptor complex in the homologues TgAMA1 and PfAMA1 [27,28], could be completely traced in both molecules except for the short region Gly328-Ser332 (Fig 2A). Nonetheless, the high temperature factors of this region indicate a propensity to structural mobility.


Crystal structure of Plasmodium knowlesi apical membrane antigen 1 and its complex with an invasion-inhibitory monoclonal antibody.

Vulliez-Le Normand B, Faber BW, Saul FA, van der Eijk M, Thomas AW, Singh B, Kocken CH, Bentley GA - PLoS ONE (2015)

Structure of domains 1 and 2 of PkAMA1 in the non-complexed form.The structure of PkAMA1 (molecule B) is shown in ribbon representation with Domain 1 in green and Domain 2 in light brown. The Domain 2 loop is shown in red and the c-myc tail is shown in mauve. The N- and C-termini are indicated by N and C, respectively. A gap occurs within the D2 loop since the protein could not be traced from residues Gly328 to Ser332.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401722&req=5

pone.0123567.g001: Structure of domains 1 and 2 of PkAMA1 in the non-complexed form.The structure of PkAMA1 (molecule B) is shown in ribbon representation with Domain 1 in green and Domain 2 in light brown. The Domain 2 loop is shown in red and the c-myc tail is shown in mauve. The N- and C-termini are indicated by N and C, respectively. A gap occurs within the D2 loop since the protein could not be traced from residues Gly328 to Ser332.
Mentions: The free PkAMA1 protein crystallized in space group C2 with two molecules (A and B) in the asymmetric unit and the structure was refined at 2.45 Å resolution (Table 1, Table 2). The polypeptide chain of molecule A was traced from Ser52 to Glu397 (thus including eight residues of the c-myc tag), with main-chain gaps Ala131-Asp132, Ser212-Lys215 and Gly328-Asn331 due to conformational mobility. Molecule B (Fig 1) was built from Ser52 to Asp398 with main-chain gaps Ser212-Ala217 and Gly328-Ser332. The two molecules are very similar, with an r.m.s.d. of 0.34 Å in Cα positions over the 332 common residues in the PkAMA1 sequence. The D2 loop of PkAMA1, which is displaced upon binding of the RON2 component of the RON receptor complex in the homologues TgAMA1 and PfAMA1 [27,28], could be completely traced in both molecules except for the short region Gly328-Ser332 (Fig 2A). Nonetheless, the high temperature factors of this region indicate a propensity to structural mobility.

Bottom Line: R31C2 inhibits binding of the Rhoptry Neck Protein 2 (RON2) receptor by steric blocking of the hydrophobic groove and by preventing the displacement of the D2 loop which is essential for exposing the complete binding site on AMA1.PkAMA1 is much less polymorphic than the P. falciparum and P. vivax orthologues.Unlike these two latter species, there are no polymorphic sites close to the RON2-binding site of PkAMA1, suggesting that P. knowlesi has not developed a mechanism of immune escape from the host's humoral response to AMA1.

View Article: PubMed Central - PubMed

Affiliation: Institut Pasteur, Unité d'Immunologie Structurale, Département de Biologie Structurale et Chimie, Paris, France; CNRS URA 2185, Paris, France.

ABSTRACT
The malaria parasite Plasmodium knowlesi, previously associated only with infection of macaques, is now known to infect humans as well and has become a significant public health problem in Southeast Asia. This species should therefore be targeted in vaccine and therapeutic strategies against human malaria. Apical Membrane Antigen 1 (AMA1), which plays a role in Plasmodium merozoite invasion of the erythrocyte, is currently being pursued in human vaccine trials against P. falciparum. Recent vaccine trials in macaques using the P. knowlesi orthologue PkAMA1 have shown that it protects against infection by this parasite species and thus should be developed for human vaccination as well. Here, we present the crystal structure of Domains 1 and 2 of the PkAMA1 ectodomain, and of its complex with the invasion-inhibitory monoclonal antibody R31C2. The Domain 2 (D2) loop, which is displaced upon binding the Rhoptry Neck Protein 2 (RON2) receptor, makes significant contacts with the antibody. R31C2 inhibits binding of the Rhoptry Neck Protein 2 (RON2) receptor by steric blocking of the hydrophobic groove and by preventing the displacement of the D2 loop which is essential for exposing the complete binding site on AMA1. R31C2 recognizes a non-polymorphic epitope and should thus be cross-strain reactive. PkAMA1 is much less polymorphic than the P. falciparum and P. vivax orthologues. Unlike these two latter species, there are no polymorphic sites close to the RON2-binding site of PkAMA1, suggesting that P. knowlesi has not developed a mechanism of immune escape from the host's humoral response to AMA1.

Show MeSH
Related in: MedlinePlus