A TYPE-I PERITROPHIC MATRIX PROTEIN FROM THE MALARIA VECTOR ANOPHELES-GAMBIAE BINDS TO CHITIN - CLONING, EXPRESSION, AND CHARACTERIZATION

Upon feeding, mosquito midguts secrete the peritrophic matrix (PM), an extracellular chitin-containing envelope that completely surrounds th e blood meal. Because the malaria parasite must cross the PM to comple te its life cycle in the mosquito, the PM is a potential barrier for m alaria transmission. By antibody screening of an expression library we have identified and partially characterized a cDNA encoding a putativ e PM protein, termed Anopheles gambiae adult peritrophin 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 gu t, and not in any other tissues or at any other stages of development. The predicted amino acid sequence indicates that it has two tandem ch itin-binding domains that share high sequence similarity with each oth er and also with the chitin-binding domain of an adult gut-specific ch itinase from the same organism. The presumed ability of Ag-Aper1 to bi nd chitin was verified by a functional assay with the baculovirus-expr essed recombinant protein. Ag-Aper1 did bind to chitin but not to cell ulose, indicating that Ag-Aper1 binds chitin specifically. The double chitin-binding domain organization of Ag-Aper1 suggests that each prot ein molecule is able to link two chitin polymer chains. Hence, this pr otein is likely to act as a molecular linker that connects PM chitin f ibrils into a three-dimensional network.