title: Fine mapping of an epitope recognized by an invasion-inhibitory monoclonal antibody on the malaria vaccine candidate apical membrane antigen 1.
abstract: Antibodies that inhibit red blood cell invasion by the Plasmodium merozoite block the erythrocytic cycle responsible for clinical malaria. The invasion-inhibitory monoclonal antibody (mAb) 4G2 recognizes a conserved epitope in the ectodomain of the essential Plasmodium falciparum microneme protein and vaccine candidate, apical membrane antigen 1 (PfAMA1). Here we demonstrate that purified Fab fragments of 4G2 inhibit invasion markedly more efficiently than the intact mAb, suggesting that the invasion-inhibitory activity of this mAb is not due solely to steric effects and that the epitope lies within a functionally critical region of the molecule. We have taken advantage of a synthetic gene encoding a modified form of PfAMA1, and existing x-ray crystal structure data, to fully characterize this epitope. We first validate the gene by demonstrating that it fully complements the function of the authentic gene in P. falciparum. We then use it to identify a group of residues within the previously described domain II loop of PfAMA1 that are critical for recognition by mAb 4G2 and demonstrate that the epitope lies exclusively within this loop with no contributions from residues in other domains of the molecule. This is the first complete characterization of a conserved invasion-inhibitory epitope on PfAMA1. Our results will aid in the design of subunit vaccines designed to generate a broadly effective, focused anti-PfAMA1 protective immune response and may help elucidate the function of PfAMA1.
authors.affiliation: Division of Parasitology, National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom.
authors.forename: Christine R
authors.initials: CR
authors.lastname: Collins
authors.forename: Chrislaine
authors.initials: C
authors.lastname: Withers-Martinez
authors.forename: Graham A
authors.initials: GA
authors.lastname: Bentley
authors.forename: Adrian H
authors.initials: AH
authors.lastname: Batchelor
authors.forename: Alan W
authors.initials: AW
authors.lastname: Thomas
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Blackman
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D000953:Antigens, Protozoan / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D019556:COS Cells; D002522:Chlorocebus aethiops; D018604:Epitope Mapping; D004912:Erythrocytes / Q000469:parasitology; D017780:Malaria Vaccines / Q000276:immunology*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D051379:Mice; D010963:Plasmodium falciparum / Q000276:immunology*; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D000953:Antigens, Protozoan; D017780:Malaria Vaccines; D008565:Membrane Proteins; D015800:Protozoan Proteins; C090077:apical membrane antigen I, Plasmodium