Identification of a cathepsin D potentially involved in H2A cleavage from scallop Chlamys farreri.

We report here a cDNA and its deduced amino acid sequence encoding a cathepsin D-like, aspartic protease from Chlamys farreri (denoted as CfCD) by expressed sequence tag and rapid amplification of cDNA ends techniques. The cDNA of CfCD consisted of 1,810 nucleotides with a canonical polyadenylation signal sequence AATAAA and a polyA tail, encoding a short signal peptide of 18 amino acids, a pro-enzyme peptide of 29 amino acid residues, and a mature enzyme of 349 residues. The deduced amino acid sequence of CfCD was significant homology to CDs from human, fish and invertebrates. Two conserved catalytic motifs (VFDTGSSNLWV and AIADTGTSLLVG) and two potential N-glycosylation sites were also identified in the deduced amino acid sequence of CfCD. All this characteristics indicated CfCD should be a member of CDs family. The mRNA spatial expression of CfCD in mantle, gonad, gill, hemocytes, hepatopancreas and adductor muscle was examined by quantitative real-time PCR. mRNA transcripts of CfCD could be detected in all tissues with the highest expression level in hepatopancreas. After 8 h Vibrio anguillarum challenge, the expression level of CfCD changed significantly in all examined tissues except mantle (P = 0.183) and hemocytes (P = 0.069). The information generated in the present study would be helpful for future studies aiming at investigating the detailed functions of cathepsin D from marine invertebrates.