Distribution of Chitinolytic Enzymes in the Organs and cDNA Cloning of Chitinase Isozymes from the Liver of Golden Cuttlefish Sepia esculenta

The distribution of chitinolytic enzymes in eight organs of the golden cuttlefish Sepia esculenta was determined. Chitinase activity (activity of endo-type chitinolytic enzyme) was measured using pNP-(GlcNAc)n (n = 2, 3) as substrates, with high activity detected in the liver, posterior salivary gland, and stomach. β-N-acetylhexosaminidase (Hex) activity (activity of exo-type chitinolytic enzyme) was determined using pNP-(GlcNAc) as a substrate, and high activity was observed in six organs, including the liver, branchial heart, posterior salivary gland, and stomach. In addition, two chitin-binding proteins (CBP-A, CBP-B) were isolated from the liver using a chitin affinity column. Two full-length cDNAs (SeChi-1: 1484 bp; SeChi-2: 1748 bp) encoding chitinases were obtained from the liver of S. esculenta. SeChi-1 contained a 1377-bp open reading frame (ORF) encoding 459 amino acids, and SeChi-2 contained a 1656-bp ORF encoding 552 amino acids. Domain structures predicted from the deduced amino acid sequences of SeChi-1 and SeChi-2 (SeChi-1, SeChi-2) contained signal peptides, a GH Family 18 catalytic domain, one chitin binding domain (CBD) in SeChi-1, and two CBDs in SeChi-2. Proteome analysis revealed that 125 peptide residues of CBP-A were present in SeChi-1, and 116 peptide residues of CBP-B were present in SeChi-2. Organ expression analysis revealed that SeChi-1 and SeChi-2 were expressed only in the liver of S. esculenta. Phylogenetic analysis of SeChi-1, SeChi-2, and GH family 18 chitinases revealed that SeChi-2 belongs to a group of previously reported squid chitinases, while SeChi-1 does not belong to any previously reported group of mollusk chitinases.