Proteolytic processing and primary structure of Plasmodium falciparum apical membrane antigen-1.
Plasmodium falciparum apical membrane antigen-1 (PfAMA-1) is a malaria merozoite integral membrane protein that plays an essential but poorly understood role in invasion of host erythrocytes. The PfAMA-1 ectodomain comprises three disulfide-constrained domains, the first of which (domain I) is preceded by an N-terminal prosequence. PfAMA-1 is initially routed to secretory organelles at the apical end of the merozoite, where the 83-kDa precursor (PfAMA-1(83)) is converted to a 66-kDa form (PfAMA-1(66)). At about the time of erythrocyte invasion, PfAMA-1(66) selectively translocates onto the merozoite surface. Here we use direct microsequencing and mass spectrometric peptide mass fingerprinting to characterize in detail the primary structure and proteolytic processing of PfAMA-1. We have determined the site at which processing takes place to convert PfAMA-1(83) to PfAMA-1(66) and have shown that both species possess a completely intact and unmodified transmembrane and cytoplasmic domain. Following relocation to the merozoite surface, PfAMA-1(66) is further proteolytically cleaved at one of two alternative sites, either between domains II and III, or at a membrane-proximal site following domain III. As a result, the bulk of the ectodomain is shed from the parasite surface in the form of two soluble fragments of 44 and 48 kDa. PfAMA-1 is not detectably modified by the addition of N-linked oligosaccharides.
Howell
S A
SA
Division of Protein Structure and the Division of Parasitology, National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom.
Withers-Martinez
C
C
Kocken
C H
CH
Thomas
A W
AW
Blackman
M J
MJ
D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan / Q000378:metabolism*; D010450:Endopeptidases / Q000502:physiology*; D004912:Erythrocytes / Q000378:metabolism; D006031:Glycosylation; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D010449:Peptide Mapping; D010963:Plasmodium falciparum / Q000276:immunology*; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*
D000953:Antigens, Protozoan; D008565:Membrane Proteins; D010446:Peptide Fragments; D015800:Protozoan Proteins; C090077:apical membrane antigen I, Plasmodium; D010450:Endopeptidases