Molecular cloning, characterization and expression analysis of trypsin-like serine protease from triangle-shell pearl mussel (Hyriopsis cumingii).

Trypsin-like serine protease (TLS) is ubiquitous in animals and plays a number of diverse roles, including dietary protein digestion, hemolymph coagulation, antimicrobial activity and immune responses, among others. This study reports the isolation of a 1048 bp full-length cDNA sequence of TLS from triangle-shell pearl mussel (Hyriopsis cumingii), including a 12 bp 5' UTR (untranslated region), a 172 bp 3' UTR, and an open reading frame (ORF) of 864 bp by rapid amplification of cDNA ends (RACE). Bioinformatic analysis shows that the gene belongs to the trypsin-like serine protease superfamily, and contains a 15 residues N-terminal signal peptide and a conserved C-terminal domain. In comparison to other serine proteases, the catalytic triad were identified as His-98, Asp-149, and Ser-240. Quantitative real-time PCR (qPCR) showed a broad expression of the TLS gene in ten tested tissues. Time-course expression analysis demonstrated that the expression level of the TLS mRNA was significantly up-regulated in eight tested tissues (liver, intestine, gill, heart, axe foot, adductor muscle, kidney and gonad), but down-regulated in mantle and stomach after Aeromonas hydrophila injection. This is one of the results indicate that TLS may be involved in innate defense reactions against A. hydrophila in triangle-shell pearl mussel.