Structure and Bioactivity of a Modified Peptide Derived from the LPS-Binding Domain of an Anti-Lipopolysaccharide Factor (ALF) of Shrimp

The lipopolysaccharide binding domain (LBD) in anti-lipopolysaccharide factor (ALF) is the main functional element of ALF, which exhibits antimicrobial activities. Our previous studies show that the peptide LBDv, synthesized based on the modified sequence of LBD (named LBD2) from FcALF2, exhibited an apparently enhanced antimicrobial activity. To learn the prospect of LBDv application, the characteristics of LBDv were analyzed in the present study. The LBDv peptide showed higher antimicrobial and bactericidal activities compared with LBD2. These activities of the LBDv peptide were stable after heat treatment. LBDv could also exhibit in vivo antimicrobial activity to Vibrio harveyi. The LBDv peptide was found to bind bacteria, quickly cause bacterial agglutination, and kill bacteria by damaging their membrane integrity. Structure analysis showed that both LBDv and LBD2 held the β-sheet structure, and the positive net charge and amphipathicity characteristic were speculated as two important components for their antimicrobial activity. The cytotoxicity of LBDv was evaluated in cultured Spodoptera frugiperda (Sf9) cells and Cherax quadricarinatus hemocytes. More than 80% cells could survive with the LBDv concentration up to 16 μM. Collectively, these findings highlighted the potential antimicrobial mechanism of LBD peptides, and provided important information for the commercial use of LBDv in the future.