Molecular cloning of a gut-specific chitinase cDNA from the beetle Phaedoncochleariae

A cDNA encoding a chitinase of Pheadon cochleariae was isolated from a larv al gut library. The cDNA encodes a preenzyme with a putative 20 amino-acid signal peptide and a 385 amino-acid mature enzyme of calculated mass of 42. 7 kDa. Amino-acid alignment shows 24-33% identity to other insect and crust acea chitinases. The sequence lacks C-terminus domains but active site resi dues are conserved. Northern analysis localizes the mRNA to guts of feeding larvae. Southern blot analysis, with a complete cDNA probe, suggests that the P. cochleariae genome may contain several chitinase genes. Activity gel s show that two groups of chitinases are expressed in the insect. One group comprises chitinases of 30-40 kDa that are active at pH 5.0 and detected i n guts of feeding larvae and adults, as well as in pre-pupae and pupae. The other group comprises chitinases of 40-70 kDa that are more active at pH 7 .0 and are mainly expressed in pre-pupae and pupae. The biological signific ance of both groups of chitinases is discussed. (C) 1999 Elsevier Science L td. All rights reserved.