A comparative study of the genetic diversity of the 42 kDa fragment of the merozoite surface protein 1 in Plasmodium falciparum and P. vivax

We investigated the genetic diversity of the 42 kDa fragment of the merozoite surface protein 1 (MSP-1) antigen in Plasmodium falciparum and P. vivax, as well as in non-human primate malarial parasites. This fragment undergoes a proteolytic cleavage generating two fragments of 19 kDa (MSP-119) and 33 kDa (MSP-133) that are critical in erythrocyte invasion. We found that overall the MSP-133 fragment exhibits greater genetic diversity than the MSP-119 regardless of the species. We have found evidence for positive natural selection only in the human malaria parasites by comparing the rate of non-synonymous versus synonymous substitutions. In addition, we found clear differences between the two major human malaria parasites. In the case of P. falciparum, positive natural selection is acting on the MSP-119 region while the MSP-133 is neutral or under purifying selection. The opposite pattern was observed in P. vivax. Our results suggest different roles of this antigen in the host–parasite immune interaction in each of the major human malarial parasites.