title: Structure of an IgNAR-AMA1 complex: targeting a conserved hydrophobic cleft broadens malarial strain recognition.
abstract: Apical membrane antigen 1 (AMA1) is essential for invasion of erythrocytes and hepatocytes by Plasmodium parasites and is a leading malarial vaccine candidate. Although conventional antibodies to AMA1 can prevent such invasion, extensive polymorphisms within surface-exposed loops may limit the ability of these AMA1-induced antibodies to protect against all parasite genotypes. Using an AMA1-specific IgNAR single-variable-domain antibody, we performed targeted mutagenesis and selection against AMA1 from three P. falciparum strains. We present cocrystal structures of two antibody-AMA1 complexes which reveal extended IgNAR CDR3 loops penetrating deep into a hydrophobic cleft on the antigen surface and contacting residues conserved across parasite species. Comparison of a series of affinity-enhancing mutations allowed dissection of their relative contributions to binding kinetics and correlation with inhibition of erythrocyte invasion. These findings provide insights into mechanisms of single-domain antibody binding, and may enable design of reagents targeting otherwise cryptic epitopes in pathogen antigens.
authors.affiliation: CSIRO Molecular and Health Technologies, 343 Royal Parade, Parkville 3052, Australia.
authors.forename: Kylie A
authors.initials: KA
authors.lastname: Henderson
authors.forename: Victor A
authors.initials: VA
authors.lastname: Streltsov
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Coley
authors.forename: Olan
authors.initials: O
authors.lastname: Dolezal
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hudson
authors.forename: Adrian H
authors.initials: AH
authors.lastname: Batchelor
authors.forename: Aditi
authors.initials: A
authors.lastname: Gupta
authors.forename: Tao
authors.initials: T
authors.lastname: Bai
authors.forename: Vincent J
authors.initials: VJ
authors.lastname: Murphy
authors.forename: Robin F
authors.initials: RF
authors.lastname: Anders
authors.forename: Michael
authors.initials: M
authors.lastname: Foley
authors.forename: Stewart D
authors.initials: SD
authors.lastname: Nuttall
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000913:Antibodies, Protozoan / Q000737:chemistry* / Q000276:immunology; D000915:Antibody Affinity; D000953:Antigens, Protozoan / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D057927:Hydrophobic and Hydrophilic Interactions; D007135:Immunoglobulin Variable Region / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D007700:Kinetics; D016778:Malaria, Falciparum / Q000276:immunology; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019151:Peptide Library; D010963:Plasmodium falciparum / Q000276:immunology*; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D020349:Surface Plasmon Resonance
chemical_list: D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D007135:Immunoglobulin Variable Region; D008565:Membrane Proteins; D019151:Peptide Library; D015800:Protozoan Proteins; C090077:apical membrane antigen I, Plasmodium