PLASMODIUM-KNOWLESI SECONDARY PROCESSING OF THE MALARIA MEROZOITE SURFACE PROTEIN-1

Secondary processing of the Plasmodium falciparum malaria merozoite su rface protein-1 (MSP-1) is defined as a single proteolytic cleavage wi thin the carboxy-terminal membrane-bound component of the MSP-1 protei n complex on the free merozoite surface. The N-terminal cleavage produ ct (MSP-1(33)) is shed from the parasite surface along with a number o f other polypeptides, whereas the C-terminal processing product remain s bound to the merozoite surface and is the only part of MSP-1 detecta ble in the newly invaded host cell. We report that secondary processin g of MSP-1 takes place in a similar manner on invasive merozoites of t he simian malaria parasite Plasmodium knowlesi. Processing can take pl ace to a limited extent in pure isolated merozoites; however, within 1 0 min of the addition of purified invasive merozoites to rhesus erythr ocytes, processing and shedding of MSP-1 has gone to completion only i n those parasites which have undergone invasion; residual free merozoi tes remain uniformly reactive with antibodies against MSP-1(33). Succe ssful invasion is therefore associated with complete shedding of MSP-1 (33) from the merozoite surface. The nucleotide sequence of the 3' dom ain of the P. knowlesi MSP-1 gene is also presented. (C) 1996 Academic Press, Inc.