Abstract: Objective: This study aimed to analyze and predict the molecular structure and physicochemical properties of the bacteriocin gene and its encoded protein from Lactobacillus casei and to clarify the antibacterial mechanism of the bacteriocin. Methods: A variety of bioinformatics software were used to predict and analyze protein structure and function. Site-directed mutagenesis was applied to the predicted amino acid sites, and the antibacterial activities of the mutants were detected. Results: Bacteriocin from L. casei (LacA and LacB) was thermally stable, contained a secretory signal peptide and had a transmembrane region. LacA contained a typical antimicrobial domain GxxxG. The mutant vectors for V40 and I57 in LacA were constructed, and the antimicrobial activity was significantly reduced when any of these two amino acids was mutated. Conclusion: V40 and I57 could be the key amino acid residues responsible for the antibacterial activity of L. casei. This study has provided a theoretical basis for exploring the antibacterial mechanism of bacteriocin from L. casei (class IIb).

Key words: Lactobacillus casei, bacteriocin, bioinformatics, site-directed mutagenesis of amino acid residues