Molecular Characterization and Antibacterial Activity of a G-Type Lysozyme in Yellow Drum (Nibea albiflora)

Lysozyme (EC3.2.1.17) plays an important role in the immune response; as a nonspecific immune factor, it can resist causative agents. Lysozyme can be divided into c-type and g-type in fish. In a previous study, through genome-wide association analysis, the g-type lysozyme gene, which is named NaLyg in yellow drum (Nibea albiflora), was found to be a key candidate gene for disease resistance in response to Vibrio harveyi infection. The cDNA of NaLyg was 1025 bp, including four exons and three introns, and its open reading frame (ORF) had a full-length of 582 bp, encoding 193 amino acids. NaLyg was found to be conserved during evolution through bioinformatic analyses. The NaLyg protein possessed a sugar binding domain and three catalytic sites, including Glu71, Asp84 and Asp101. Quantitative qRT-PCR results confirmed that NaLyg gene mRNA was visibly increased after V. harveyi infection. The NaLyg protein purified by prokaryotic expression killed some gram-negative bacterial pathogens by inducing cell wall destruction, including V. harveyi, Aeromonas hydrophila and Edwardsiella tarda. Moreover, the NaLyg protein killed two gram-positive bacteria, Bacillus subtilis and Staphylococcus aureus. Taken together, the experimental results suggested that the NaLyg protein of N. albiflora played an important role in fighting bacterial infections.