title: Knockout of the rodent malaria parasite chitinase pbCHT1 reduces infectivity to mosquitoes.
abstract: During mosquito transmission, malaria ookinetes must cross a chitin-containing structure known as the peritrophic matrix (PM), which surrounds the infected blood meal in the mosquito midgut. In turn, ookinetes produce multiple chitinase activities presumably aimed at disrupting this physical barrier to allow ookinete invasion of the midgut epithelium. Plasmodium chitinase activities are demonstrated targets for human and avian malaria transmission blockade with the chitinase inhibitor allosamidin. Here, we identify and characterize the first chitinase gene of a rodent malaria parasite, Plasmodium berghei. We show that the gene, named PbCHT1, is a structural ortholog of PgCHT1 of the avian malaria parasite Plasmodium gallinaceum and a paralog of PfCHT1 of the human malaria parasite Plasmodium falciparum. Targeted disruption of PbCHT1 reduced parasite infectivity in Anopheles stephensi mosquitoes by up to 90%. Reductions in infectivity were also observed in ookinete feeds-an artificial situation where midgut invasion occurs before PM formation-suggesting that PbCHT1 plays a role other than PM disruption. PbCHT1 null mutants had no residual ookinete-derived chitinase activity in vitro, suggesting that P. berghei ookinetes express only one chitinase gene. Moreover, PbCHT1 activity appeared insensitive to allosamidin inhibition, an observation that raises questions about the use of allosamidin and components like it as potential malaria transmission-blocking drugs. Taken together, these findings suggest a fundamental divergence among rodent, avian, and human malaria parasite chitinases, with implications for the evolution of Plasmodium-mosquito interactions.
authors.affiliation: Department of Biology, Imperial College of Science, Technology, and Medicine, London SW7 2AZ, United Kingdom. j.dessens@ic.ac.uk
authors.forename: J T
authors.initials: JT
authors.lastname: Dessens
authors.forename: J
authors.initials: J
authors.lastname: Mendoza
authors.forename: C
authors.initials: C
authors.lastname: Claudianos
authors.forename: J M
authors.initials: JM
authors.lastname: Vinetz
authors.forename: E
authors.initials: E
authors.lastname: Khater
authors.forename: S
authors.initials: S
authors.lastname: Hassard
authors.forename: G R
authors.initials: GR
authors.lastname: Ranawaka
authors.forename: R E
authors.initials: RE
authors.lastname: Sinden
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D000852:Anopheles / Q000469:parasitology*; D002688:Chitinases / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D006790:Host-Parasite Interactions; D008288:Malaria / Q000469:parasitology; D008969:Molecular Sequence Data; D010962:Plasmodium berghei / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D017422:Sequence Analysis, DNA
chemical_list: D002688:Chitinases