A novel chitin-binding protein from the vestimentiferan Riftia pachyptila interacts specifically with beta-chitin - Cloning, expression, and characterization

A cDNA from Riftia pachyptila was cloned. It encodes a novel 21.3-kDa prote in from the worm protective tube, named RCBP (for Riftia chitin-binding pro tein). On the basis of partial tube-peptide sequences previously obtained, experiments using reverse transcriptase-mediated polymerase chain reaction and rapid amplification of cDNA ends led to the complete cDNA sequence. Ana lysis of its deduced amino acid sequence shows the presence of two chitin-b inding domains. These domains are closely related to type 2 chitin-binding domains that are restricted to the animal kingdom. We showed by affinity as say and immunogold labeling that RCBP is the first protein so far known tha t binds specifically beta -chitin and that is unable to bind the most commo n alpha -form found in chitin secreting animals. The RCBP mRNA was found to be present in specific epidermal cells from the worm body wall, but never in the chitin-secreting gland cells. This unexpected result clearly indicat es that this tube protein is synthesized in specialized areas of the outer epithelium and that at least two different tissues are involved in this exo skeleton synthesis.