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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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Germline sequences and somatic mutations of the R31C2 variable domains.(A) Amino acid and nucleotide sequences of the R31C2 VL domain compared with the Vκ and Jκ germline genes. (B) Amino acid and nucleotide sequences of the R31C2 VH domain compared with the VH, D and JH germline genes.
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pone.0123567.g005: Germline sequences and somatic mutations of the R31C2 variable domains.(A) Amino acid and nucleotide sequences of the R31C2 VL domain compared with the Vκ and Jκ germline genes. (B) Amino acid and nucleotide sequences of the R31C2 VH domain compared with the VH, D and JH germline genes.

Mentions: The VH and VL sequences were compared with germline sequences using the International Immunogenetics Information server [48] (Fig 5). The VL domain derives from the Vκ germline gene IGKV14S1 (98.9% identity) and the J gene segment IGKJ5. Five somatic mutations in the amino acid sequence are present in the regions encoded by the Vκ and Jκ gene segments but none of these make direct contacts with PkAMA1. The VH domain derives from the germline gene IGHV5S36 (92.7% identity), the IGHD1-6 D minigene and the IGHJ2 J gene segment. Eighteen somatic amino acid mutations are present, five of which contact PkAMA1: Tyr50Thr, Gly53Ser, Gly55Ser and Ser56Arg in CDR-H2 and Asp100bGlu in CDR-H3. The higher selection pressure on VH probably reflects the significantly more important role of this domain in binding to PkAMA1. The somatic mutation Tyr50Thr leads to a hydrogen bond between Oγ and the glutamate group of Glu173, which would not be sterically possible for the germline residue tyrosine. The mutation Gly55Ser does not lead to additional polar interactions but probably improves the complementarity at the antibody-antigen interface. The mutation Ser56Arg appears to have the most significant impact in the affinity maturation of R31C2 as this antibody residue forms a salt bridge to Glu81 and Asp174 of PkAMA1. CDR-H3 residue Arg95, which forms a salt bridge to Glu173, probably results from nucleotide deletions and additions occurring at the junction between VH and D (used in the third reading frame).


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)

Germline sequences and somatic mutations of the R31C2 variable domains.(A) Amino acid and nucleotide sequences of the R31C2 VL domain compared with the Vκ and Jκ germline genes. (B) Amino acid and nucleotide sequences of the R31C2 VH domain compared with the VH, D and JH germline genes.
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Related In: Results  -  Collection

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

pone.0123567.g005: Germline sequences and somatic mutations of the R31C2 variable domains.(A) Amino acid and nucleotide sequences of the R31C2 VL domain compared with the Vκ and Jκ germline genes. (B) Amino acid and nucleotide sequences of the R31C2 VH domain compared with the VH, D and JH germline genes.
Mentions: The VH and VL sequences were compared with germline sequences using the International Immunogenetics Information server [48] (Fig 5). The VL domain derives from the Vκ germline gene IGKV14S1 (98.9% identity) and the J gene segment IGKJ5. Five somatic mutations in the amino acid sequence are present in the regions encoded by the Vκ and Jκ gene segments but none of these make direct contacts with PkAMA1. The VH domain derives from the germline gene IGHV5S36 (92.7% identity), the IGHD1-6 D minigene and the IGHJ2 J gene segment. Eighteen somatic amino acid mutations are present, five of which contact PkAMA1: Tyr50Thr, Gly53Ser, Gly55Ser and Ser56Arg in CDR-H2 and Asp100bGlu in CDR-H3. The higher selection pressure on VH probably reflects the significantly more important role of this domain in binding to PkAMA1. The somatic mutation Tyr50Thr leads to a hydrogen bond between Oγ and the glutamate group of Glu173, which would not be sterically possible for the germline residue tyrosine. The mutation Gly55Ser does not lead to additional polar interactions but probably improves the complementarity at the antibody-antigen interface. The mutation Ser56Arg appears to have the most significant impact in the affinity maturation of R31C2 as this antibody residue forms a salt bridge to Glu81 and Asp174 of PkAMA1. CDR-H3 residue Arg95, which forms a salt bridge to Glu173, probably results from nucleotide deletions and additions occurring at the junction between VH and D (used in the third reading frame).

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