Gene families encoding proteins with chitin-binding domains in Tribolium castaneum: domain organization, phylogenetic analysis and expression during development

Chitin maintains the structural integrity of both the insect cuticle and the peritrophic matrix (PM), by interacting with proteins with two major classes of chitin binding domains (CBDs). This study is focused on the characterization and expression of genes encoding proteins with six cysteine−containing CBDs of Peritrophin−A subfamily (ChtBD2=CBM_14=Pfam 01607), in the red flour beetle, Tribolium castaneum. An exhaustive bioinformatics search of the genome of T. castaneum identified 28 genes encoding proteins with one to fourteen ChtBD2. Using phylogenetic analyses and domain organization, these proteins were classified into two large families. One−group, Peritrophic Matrix Proteins (PMPs), included 11 proteins with multiple CBDs closely related to those found in peritrophins of the PM and exhibit midgut−specific expression restricted to the actively feeding larval and adult stages. The second group Cuticular Proteins Analogous to Peritrophins (CPAPs)includes 18 proteins, eight of which are closely related the gasp/obstructor family of genes in Drosophila. The eight proteins of this family are expressed predominantly in the carcass, throughout all developmental stages. RNAi for many of these genes shows lethal phenotypes that manifest at different developmental stages. Our data provide experimental support for evolutionary divergence and specialization in the functions of ChtBD2-containing proteins.