Identification of antibacterial and chemotactic activities of a novel NK-lysin peptide from Lateolabrax japonicus.

NK-lysin is an effective antimicrobial peptide secreted by natural killer (NK) cells and cytotoxic T lymphocytes. Although numerous studies have been conducted on NK-lysin, its biological functions have not yet been comprehensively catalogued. In this study, a novel NK-lysin peptide, NKLj27, located in the SapB domain of Japanese seabass Lateolabrax japonicus, was identified and synthesized, and its antibacterial and chemotactic activities were investigated. Bioinformatic analyses showed that NKLj27 shared 66.67-79.17% sequence homology with known teleost NK-lysin peptides, and the spatial structure prediction of NKLj27 indicated that it was mainly composed of α-helices. A subsequent antibacterial assay demonstrated that NKLj27 exhibits potent activity against Staphylococcus aureus, Micrococcus luteus, Vibrio litoralis, V. alginolyticus, Listonella anguillarum, Escherichia coli, V. harveyi, and V. scophthalmi. During the interaction with V. alginolyticus, NKLj27 changed the cell membrane permeability, causing leakage of cellular contents, while the cell membrane structure remained basically intact; subsequently, NKLj27 penetrated into the cytoplasm and acted on bacterial nucleic acids. It first bound to bacterial genomic DNA and RNA, then caused their retardation and degradation, and following incubation, it changed the physical conformation of the DNA molecules. The in vivo experiments showed that NKLj27 significantly reduced V. alginolyticus load in fish tissues. At the cellular level, NKLj27 also exhibited chemotactic activity on epithelioma papulosum cyprini cells. In summary, these results provide new insights into the functions of NK-lysin peptides in teleosts and show the potential of using NKLj27 in aquaculture for bacterial disease control.