Structure-activity analysis and biological studies of chensinin-1b analogues

Chensinin-1b shows a potent and broad-spectrum bactericidal activity and no hemolytic activity and thus is a potential therapeutic agent against bacterial infection. The NMR structure of chensinin-1b consists of a partially α-helical region (residues 8–14) in a membrane-mimic environment that is distinct from other common antimicrobial peptides. However, further analysis of the structural features of chensinin-1b is required to better understand its bactericidal activity. In this study, a series of N- and C-terminally truncated or amino acid-substituted chensinin-1b analogues were synthesized. Next, the bactericidal activity and bacterial membrane effects of the analogues were investigated. The results indicated that the N-terminal residues play a more significant role than the C-terminal residues in the antimicrobial activity of chensinin-1b. The removal of five amino acids from the C-terminus of chensinin-1b did not affect its biological properties, but helix disruption significantly decreased bactericidal activity. The substitution of positively charged residues increased the helicity and antimicrobial activity of the peptide. We also identified a novel analogue [R4,R10]C1b(3–13) that exhibited similar bactericidal properties with its parent peptide chensinin-1b. Electrostatic interactions between the selected analogues and lipopolysaccharides or cells were detected using isothermal titration calorimetry or zeta potential. The thermodynamic parameters ΔH and ΔS for [R4,R10]C1b(3–13) were −20.48kcalmol−1 and −0.0408kcalmol−1deg−1, respectively. Chensinin-1b yielded similar results of −26.36kcalmol−1 and −0.0559kcalmol−1deg−1 for ΔH and ΔS, respectively. These results are consistence with their antimicrobial activities. Lastly, membrane depolarization studies showed that selected analogues exerted bactericidal activity by damaging the cytoplasmic membrane.