Chondrichthyes Chitinase: Molecular Cloning, Distribution, and Phylogenetic Analysis

Abstract

We have previously reported the presence of three types of chitinase (acidic fish chitinase-1: AFCase-1, acidic fish chitinase-2: AFCase-2, fish chitinase-3: FCase-3) in Actinopterygii. In the present research, we report the identification of the novel chitinase genes HjChi (ORF: 1380 bp) and DkChi (ORF: 1440 bp) from the stomach of Chondrichthyes, Japanese bullhead shark (Heterodontus japonicas) and Kwangtung skate (Dipturus kwangtungensis), respectively. Organ-specific expression analysis identified the stomach-specific expression of HjChi, whereas DkChi was expressed widely in all organs. Chitinase activity was measured using pNP-(GlcNAc)n (n = 2, 3) as a substrate and β-N-acetylhexosaminidase (Hex) activity was measured using pNP- GlcNAc. Relatively high values of chitinase activity were observed in the stomach, spleen, and gonads of the Japanese bullhead shark, H. japonicas, compared with that observed in the stomach of the Kwangtung skate D. kwangtungensis. However, Hex activity was detected throughout the body of both species. The optimal pH of chitinase in both the Japanese bullhead shark, H. japonicas, and the Kwangtung skate, D. kwangtungensis, were 3.5 - 5.5 and 3.5 - 4.0, respectively, and 4.0 for Hex in both species. Phylogenetic analysis revealed that Chondrichthyes chitinase forms a unique group (Chondrichthyes chitinase). These results suggested that the possibility of the formation of chitinase groups for each class in the phylogenetic analysis based on the observation of class-specific chitinase.