Peptide Fragments of a β-Defensin Derivative with Potent Bactericidal Activity

Abstract

␤-Defensins are known to be both antimicrobial and able to chemoattract various immune cells. Although the sequences of paralogous genes are not highly conserved, the core defensin structure is retained. Defb14-1C V has bactericidal activity similar to that of its parent peptide (murine ␤-defensin Defb14) despite all but one of the canonical six cysteines being replaced with alanines. The 23-amino-acid N-terminal half of Defb14-1C V is a potent antimicrobial while the C-terminal half is not. Here, we use a library of peptide derivatives to demonstrate that the antimicrobial activity can be localized to a particular region. Overlapping fragments of the N-terminal region were tested for their ability to kill Gram-positive and Gram-negative bacteria. We demonstrate that the most N-terminal fragments (amino acids 1 to 10 and 6 to 17) are potent antimicrobials against Gram-negative bacteria whereas fragments based on sequence more C terminal than amino acid 13 have very poor activity against both Gram-positive and -negative types. We further test a series of N-terminal deletion peptides in both their monomeric and dimeric forms. We find that bactericidal activity is lost against both Gram types as the deletion region increases, with the point at which this occurs varying between bacterial strains. The dimeric form of the peptides is more resistant to the peptide deletions, but this is not due just to increased charge. Our results indicate that the primary sequence, together with structure, is essential in the bactericidal action of this ␤-defensin derivative peptide and importantly identifies a short fragment from the peptide that is a potent bactericide.

Cytokeratins mediate epithelial innate defense through their antimicrobial properties

“…Firstly, antimicrobial activity of K6A-derived peptides was unaffected by changes in charge or predicted hydrophobic moment, and all but one (36-mer) lacked an α-helical secondary structure in conditions mimicking the environment of bacterial cell membranes. This contrasts with many other previously identified types of antimicrobial peptide for which cationic charge, hydrophobicity, and α-helix formation are important criteria in their antimicrobial function (25,34). Proposed mechanisms for these requirements include binding to anionic bacterial cell membranes with disruption involving pore formation.…”

“…However, other examples exist of truncated antimicrobial peptides retaining activity, including some of the defensins and LL-37 (25,26). Two other vari- (E) Combined 2-photon confocal imaging showed increased adherence of P. aeruginosa (PAO1-GFP, green) to whole corneas previously treated with siRNA for murine K6A compared with those treated with scrambled control.…”

Will new generations of modified antimicrobial peptides improve their potential as pharmaceuticals?

“…Distinct regions within β-defensins appear to be related to both the spectrum and potency of antimicrobial activity [89–91]. In the murine β-defensin Defb14, congeners of the N-terminus have potent antimicrobial activity for Gram-negative bacteria, and congeners of the C-terminus have poor antimicrobial activity against Gram-negative and Gram-positive bacteria [91].…”

“…In the murine β-defensin Defb14, congeners of the N-terminus have potent antimicrobial activity for Gram-negative bacteria, and congeners of the C-terminus have poor antimicrobial activity against Gram-negative and Gram-positive bacteria [91]. In HBD1 and HBD3, the internal regions of HBD1 and the C-terminal region of HBD3 are critical for antibacterial activity at high salt concentrations [90].…”

Cytotoxicity and the effect of cationic peptide fragments against cariogenic bacteria under planktonic and biofilm conditions

“…The peptide fragments LL-3(LLGDFFRKSKEKIGK EFKRIVQRIKDFLRNLVPRTES) derived from hCAP-18 (Ji et al 2007); Def14-1C V (6-17) or D6-17 (LRKFFARIRGGR) and Defb14-1C V (1-23) or D1-23 (FLPKTLRKFFARI RGGRAAVLNA) derived from Defb14, the mouse ortholog of human β-defensin-3 (Reynolds et al 2010), were purchased from Invitrogen (Life Technologies, Carlsbad, CA, USA). Defb14-1C V is a peptide in which the cysteines have been replaced with percentages, which represented the inhibitory effect of the mitochondrial activity of the cells by the peptides/CHX.…”