Characterization of a molting-related chitinase from a land crab, Chiromantes haematocheir

Chitinases play an important role in many biological processes, including molting, digestion, and immunity in crustaceans. This study represents an attempt to apply chitinases in the field of biotechnology, detecting chitinase mRNAs from a land crab, Chiromantes haematocheir, via transcriptome analysis and analyzing their properties. Seven chitinase genes were detected from the RNA-seq data of midgut glands. Among these genes, TRINITY_DN29294 transcripts accounted for virtually all of total expression of the chitinases. The 29294 cDNA contained a 1467 bp open reading frame, coded for 488 amino acid residues, and was classified into the GH18 chitolectin chitotriosidase and the group 3 crab chitinase. The expression of the 29294-chitinase mRNA was detected in all tissues, with the highest levels expressed in the midgut glands. The transcripts increased significantly in the early post-molted crab compared to the non-molting crab. These results suggest that 29294-chitinase plays important roles in the molting process. While the recombinant 29294-chitinase over-produced in Escherichia coli did not show any activity, the enzyme expressed in Pichia pastoris exhibited sufficient activity. The 29294-chitinase had its optimal pH 3.0. The optimal temperature was relatively high at 45 °C. The enzyme hydrolyzed both soluble and crystalline substrates.