A Lysin motif (LysM)-containing protein from Hong Kong oyster, Crassostrea hongkongensis functions as a pattern recognition protein and an antibacterial agent

Lysin motif (LysM)-containing proteins are a family of carbohydrate-binding modules and are generally regarded as chitin- and peptidoglycan-binding proteins. In the present study, a novel LysM-containing protein, designated as ChLysM, was cloned and identified in a marine mollusk, Crassostrea hongkongensis. The full-length cDNA of ChLysM consists of 1129 bp, with an open reading frame of 861 bp encoding a 286 amino acid polypeptide. The deduced protein had a calculated molecular mass of 32.66 kDa and a pI of 8.16. SMART analysis indicated that ChLysM has one Lysin motif and a transmembrane region in the C-terminal residues. Tissue distribution analysis of ChLysM revealed high expression in gills and hemocytes. The upregulated transcripts of ChLysM in response to bacterial challenge suggest that ChLysM is involved in innate immunity against pathogen infection. The recombinant protein of ChLysM was found to bind to various kinds of peptidoglycans from Staphylococcus aureus, Bacillus subtilis and Saccharomyces cerevisiae, as well as binding strongly to both Gram-positive and Gram-negative bacteria. Moreover, ChLysM displayed broad-spectrum antibacterial activity against both Gram-positive bacteria (S. aureus and S. haemolyticus) and Gram-negative bacteria (Escherichia coli and Vibrio alginolyticus). Collectively, these results indicate that ChLysM is a pattern recognition molecule with bacterial growth-inhibiting activity in immune defense of C. hongkongensis.