Molecular Mechanisms that Govern the Specificity of Sushi Peptides for Gram-Negative Bacterial Membrane Lipids

Abstract

Factor C-derived Sushi peptides (S1 and S3) have been shown to bind lipopolysaccharide (LPS) and inhibit the growth of Gram-negative bacteria but do not affect mammalian cells. On the premise that the composition of membrane phospholipids differs between the microbial and human cells, we studied the modes of interaction between S1 and S3 and the bacterial membrane phospholipids, POPG, in comparison to that with the mammalian cell membrane phospholipids, POPC and POPE. S1 exhibits specificity against POPG, suggesting its preference for bacterial anionic phospholipids, regardless of whether the phospholipids form vesicles in a solution or a monolayer on a solid surface. The specificity of the Sushi peptides for POPG is a consequence of the electrostatic and hydrophobic forces. The unsaturated nature of POPG confers fluidity to the lipid layer, and being in the proximity of LPS in the microenvironmental milieu, POPG probably enhances the insertion of the peptide-LPS complex into the bacterial inner membrane. Furthermore, during its interaction with POPG, the S1 peptide underwent a transition from random to alpha-helical coil, while S3 became a mixture of beta-sheet and alpha-helical structures. This differential structural change in the peptides could be responsible for their different modes of disruption of POPG vesicles. Conceivably, the selectivity for POPG spares the mammalian membranes from undesirable effects of antimicrobial peptides, which could be helpful in designing and developing a new generation of antibiotics and in offering some clues about the specific function of Factor C, a LPS biosensor.

The Sushi peptides: structural characterization and mode of action against Gram-negative bacteria

“…Thus, the structure-activity relationship of S1 was studied using biophysical methods. It was shown that under physiological conditions, S1 peptide was monomeric with a molecular mass of 4 kDa, and it adopted a random structure in aqueous solution [28]. This is similar to the secondary structure reported for magainin and other monomeric peptides [127 -129].…”

“…This possibility is corroborated by observations that mutations of the N-terminii of the respective Sushi peptides by introducing two extra lysine residues resulted in an increase in LPS-neutralizing activity [115]. Recent findings suggest that the initial charge interaction is responsible for the selective binding between the peptides and the bacterial membrane [28]. Moreover, this electrostatic difference between the phospholipids accounts partly for the charge difference between the mammalian and GNB cell membranes, ultimately contributing to the specificity of the antimicrobial peptides, which preferentially bind to the exposed anionic surface of bacterial membranes but not to the zwitterionic amphiphiles present in the extracellular monolayer of mammalian plasma membranes.…”

“…This plot is based on information obtained from the scientific literature [19,27]. Reprinted with permission from Li et al [28]. Copyright 2007 American Chemical Society.…”

“…Given that S1 and S3 peptides are derived from different LPS-binding domains of the Factor C molecule [115], and that S1 and S3 resume unique structural properties in the presence of LPS [28,133], it appears that, in vivo, Factor C probably harbors versatile modes of interaction against GNB where the a-helical and b-sheet structures of the Sushi 1 and 3 domains, respectively, bind LPS and conceivably cooperate to confer an extremely sensitive LPSbiosensor against Gram-negative infection [107,143,144].…”

Iterative Antimicrobial Candidate Selection from Informed D‐/L‐Peptide Dimer Libraries

“…To mimic the overall negatively charged outer envelope of bacteria, we used negatively charged small unilamellar lipid vesicles. [35,45] In this lipid C . These data might indicate partial folding, [24,[28][29][30][31] which could become more prominent in a genuine cell membrane.…”