Molecular characterization, expression, and antibacterial activity of a c-type lysozyme isolated from the manila clam, Ruditapes philippinarum.

Lysozyme is an antibacterial enzyme that is widely distributed in nature and plays an important role in the prevention of bacterial infections. In this study, a c-type lysozyme (designated as "RpCLYZ") was cloned and characterized from the manila clam, Ruditapes philippinarum. The full-length cDNA was 619 bp with an open reading frame (ORF) of 447 bp, and encoded a polypeptide of 148 amino acids with a calculated molecular mass of 17.0 kDa and an isoelectric point of 4.83. RpCLYZ was found to share high sequence similarity with c-type lysozymes from other invertebrates. The mRNA transcript of RpCLYZ was universally expressed in a wide range of tissues, especially in gills and mantle. Challenge with Vibrio anguillarum, significantly induced mRNA expression of RpCLYZ, which reached a maximum level 48 h after bacterial challenge. Recombinant RpCLYZ (rRpCLYZ) exhibited antibacterial activities against both Gram-positive and Gram-negative bacteria. Additionally, the optimal pH and temperature for rRpCLYZ activity were determined to be 4.5 and 20 °C, respectively. These results suggest that RpCLYZ participates in innate immune responses against bacterial invasion.