A Type I Peritrophic Matrix Protein from the Malaria VectorAnopheles gambiae Binds to Chitin

Abstract

Upon feeding, mosquito midguts secrete the peritro- phic matrix (PM), an extracellular chitin-containing en- velope that completely surrounds the blood meal. Be- cause the malaria parasite must cross the PM to complete its life cycle in the mosquito, the PM is a po- tential barrier for malaria transmission. By antibody screening of an expression library we have identified and partially characterized a cDNA encoding a putative PM protein, termed Anopheles gambiae adult peritro- phin 1 (Ag-Aper1). Ag-Aper1 is the first cloned PM gene from a disease vector. Northern analysis detected an abundant Ag-Aper1 transcript only in the adult gut, and not in any other tissues or at any other stages of devel- opment. The predicted amino acid sequence indicates that it has two tandem chitin-binding domains that share high sequence similarity with each other and also with the chitin-binding domain of an adult gut-specific chitinase from the same organism. The presumed ability of Ag-Aper1 to bind chitin was verified by a functional assay with the baculovirus-expressed recombinant pro- tein. Ag-Aper1 did bind to chitin but not to cellulose, indicating that Ag-Aper1 binds chitin specifically. The double chitin-binding domain organization of Ag-Aper1 suggests that each protein molecule is able to link two chitin polymer chains. Hence, this protein is likely to act as a molecular linker that connectsPMchitin fibrils into a three-dimensional network.