The chitinase PfCHT1 from the human malaria parasite Plasmodium falciparumlacks proenzyme and chitin-binding domains and displays unique substrate preferences

Within hours after the ingestion of a blood meal, the mosquito midgut epith elium synthesizes a chitinous sac, the peritrophic matrix. Plasmodium ookin etes traverse the peritrophic matrix while escaping the mosquito midgut. Ch itinases (EC 3.2.1.14) are critical for parasite invasion of the midgut: th e presence of the chitinase inhibitor, allosamidin, in an infectious blood meal prevents oocyst development. A chitinase gene, PgCHT1, recently has be en identified in the avian malaria parasite P, gallinaceum. We used the seq uence of PgCHT1 to identify a P. falciparum chitinase gene, PfCHT1, in the P. falciparum genome database. PfCHT1 differs from PgCHT1 in that the P. fa lciparum gene lacks proenzyme and chitin-binding domains. PfCHT1 was expres sed as an active recombinant enzyme in Escherichia coli. PfCHT1 shares with PgCHT1 a substrate preference unique to Plasmodium chitinases: the enzymes cleave tri- and tetramers of GlcNAc from penta- and hexameric oligomers an d are unable to cleave smaller native chitin oligosaccharides. The pH activ ity profile of PfCHT1 and its IC50 (40 nM) to allosamidin are distinct from endochitinase activities secreted by P. gallinaceum ookinetes. Homology mo deling predicts that PgCHT1 has a novel pocket in the catalytic active site that PfCHT1 lacks, which may explain the differential sensitivity of PfCHT 1 and PgCHT1 to allosamidin. PfCHT1 may be the ortholog of a second, as yet unidentified, chitinase gene of P, gallinaceum. These results may allow us to develop novel strategies of blocking human malaria transmission based o n interfering with P. falciparum chitinase.