Distinct mechanisms govern proteolytic shedding of a key invasion protein in apicomplexan pathogens

Area of Science:

• Molecular biology
• Parasitology
• Cell biology

Background:

• Apical membrane antigen-1 (AMA1) is crucial for apicomplexan parasite invasion of host cells.
• The precise role and processing of AMA1 during invasion remain incompletely understood.
• Comparative studies of AMA1 in different apicomplexans can elucidate conserved and divergent mechanisms.

Purpose of the Study:

• To investigate the processing and fate of Plasmodium falciparum AMA1 (PfAMA1) during erythrocyte invasion.
• To compare PfAMA1 processing with that of the Toxoplasma gondii orthologue, TgAMA1.
• To identify the proteases involved in AMA1 shedding and their cleavage sites.

Main Methods:

• Analysis of PfAMA1 shedding during merozoite invasion of erythrocytes.
• Comparison of PfAMA1 processing with TgAMA1 shedding from tachyzoites.
• Inhibition of PfAMA1 shedding to study alternative cleavage pathways.
• Testing PfAMA1 susceptibility to Drosophila rhomboid-1 protease.
• Detection of AMA1 on the surface of newly invaded tachyzoites.

Main Results:

• PfAMA1 ectodomain shedding is largely complete during Plasmodium invasion, primarily via juxtamembrane cleavage.
• Inhibition of normal shedding leads to intramembrane rhomboid-like cleavage of PfAMA1.
• TgAMA1 shedding occurs via cleavage within the transmembrane domain by a rhomboid-like protease.
• Unlike PfAMA1, intact TgAMA1 is detected on newly invaded tachyzoites, indicating incomplete shedding.
• A rhomboid-like protease is present on the surface of malaria merozoites.

Conclusions:

• Plasmodium and Toxoplasma exhibit distinct mechanisms for shedding AMA1 during host cell invasion.
• PfAMA1 is processed differently from TgAMA1, with Plasmodium utilizing juxtamembrane cleavage and Toxoplasma using intramembrane cleavage.
• The findings suggest the presence of a specific rhomboid-like protease involved in PfAMA1 processing during malaria parasite invasion.