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High Yield Purification of Plasmodium falciparum Merozoites For Use in Opsonizing Antibody Assays
Published on: July 17, 2014
Proteolytic processing and primary structure of Plasmodium falciparum apical membrane antigen-1
S A Howell1, C Withers-Martinez, C H Kocken
1Division of Protein Structure and the Division of Parasitology, National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom.
Abstract:
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.
Insights
Plasmodium falciparum apical membrane antigen-1 (PfAMA-1) processing was detailed, revealing its conversion to a 66-kDa form and shedding of ectodomain fragments during malaria parasite invasion.
Area of Science:
- Malaria parasite biology
- Proteomics and protein processing
- Infectious disease mechanisms
Background:
- Plasmodium falciparum apical membrane antigen-1 (PfAMA-1) is crucial for malaria parasite invasion of red blood cells.
- Its precise role and processing steps remain incompletely understood.
- PfAMA-1 is a merozoite integral membrane protein with a structured ectodomain.
Purpose of the Study:
- To elucidate the detailed primary structure and proteolytic processing of PfAMA-1.
- To identify the specific cleavage sites involved in PfAMA-1 maturation and shedding.
- To characterize the functional domains of PfAMA-1 during erythrocyte invasion.
Main Methods:
- Direct microsequencing of PfAMA-1.
- Mass spectrometric peptide mass fingerprinting.
- Analysis of protein processing intermediates and products.
Main Results:
- Identified the processing site converting the 83-kDa precursor (PfAMA-1(83)) to the 66-kDa form (PfAMA-1(66)).
- Confirmed intact transmembrane and cytoplasmic domains in both PfAMA-1 forms.
- Demonstrated PfAMA-1(66) shedding of its ectodomain into 44- and 48-kDa fragments via alternative cleavage sites.
- PfAMA-1 is not N-linked glycosylated.
Conclusions:
- PfAMA-1 undergoes sequential proteolytic cleavage events essential for its function during malaria parasite invasion.
- The shedding of PfAMA-1 ectodomain fragments is a key step in the invasion process.
- Understanding PfAMA-1 processing provides insights into potential malaria intervention strategies.
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