Identification and characterization of a novel phage-type like lysozyme from Manila clam, Ruditapes philippinarum.

A novel lysozyme gene (RpLysPh) with high similarity to the bacteriophage lysozymes was identified in Manila clam, Ruditapes philippinarum. The full length cDNA of RpLysPh is 828bp and contains a 462bp open reading frame (ORF) that codes for a 154 amino acid protein. Multiple sequence alignment analysis revealed that the three residues essential for catalytic activity in phage-type lysozyme (Glu(20), Asp(29), and Thr(35)) are conserved in RpLysPh. The comparison of the 3D models of RpLysPh and Coxiella burnetii lysozyme also suggested that the active sites involved in the binding of substrate have similar conformations. Phylogenetic analysis suggested that RpLysPh shares a similar origin with the bacterial phage-type lysozyme group. The highest level of expression of RpLysPh was observed in hemocytes, followed by mantle. Induction of RpLysPh expression was observed in gills in response to lipopolysaccharide (LPS), peptidoglycan (PGN), polyinosinic-polycytidylic acid (Poly(I:C)), and whole glucan particles (WGP) challenge. The recombinant protein of RpLysPh showed antibacterial activity against both Gram-positive and Gram-negative bacteria.