Gene structure and ookinete expression of the chitinase genes of Plasmodium vivax and Plasmodium yoelii.

After ingestion by mosquitoes, malaria parasites fertilize in the midgut and develop into motile ookinetes, which penetrate the chitin-containing peritrophic matrix and midgut epithelium cells to develop into oocysts . Chitinase activity is critical for ookinetes to penetrate the peritrophic matrix. Recently, genes encoding chitinases were identified in Plasmodium gallinaceum (pgcht1), Plasmodium falciparum (pfcht1), and Plasmodium berghei (pbcht1). Parasites with disrupted pfcht1 or pbcht1 gene loci showed reduced infectivity to the mosquitoes, confirming an important role of chitinase in parasite invasion of the mosquito, presumably at the step of penetrating the peritrophic matrix. We report here the identification of genes encoding chitinase homologues in Plasmodium vivax (pvcht1), Plasmodium knowlesi (pkcht1), Plasmodium yoelii (pycht1), and Plasmodium chabaudi (pchcht1), and demonstrate their expression in P. vivax and P. yoelii ookinetes. The predicted primary structure of the catalytic domain of PvCHT1 differs from that of human chitotriosidase, suggesting the possibility that P. vivax chitinase can be a target of blocking parasite transmission to mosquitoes through selective drug inhibition.