title: Antimicrobial activity of human β-defensin 4 analogs: insights into the role of disulfide linkages in modulating activity.
abstract: Human β-defensins (HBDs) are cationic antimicrobial peptides that are components of the innate immune system. They are characterized by three disulfide bridges. However, the number of cationic residues as well as the presence of lysine and arginine residues vary. In HBD4, the cationic residues occur predominantly in the N-terminal segment, unlike in HBD1-3. We have examined the antimicrobial activity of peptides spanning the N- and C-terminal segments of HBD4. We have introduced one, two and three disulfide bridges in the peptides corresponding to the N-terminal segments. Peptides corresponding to the N-terminal segment had identical sequences and variation was only in the number and spacing of cysteines and disulfide bridges. Antimicrobial activity to varying extents was observed for all the peptides. When two disulfide bridges were present, decrease in antimicrobial potency as well as sensitivity of activity to salt was observed. Enhanced antimicrobial activity was observed when three disulfide bridges were present. The antimicrobial potency was similar to HBD4 except against Escherichia coli and was attenuated in the presence of salt. While the presence of three disulfide bridges did not constrain the peptide to a rigid β-sheet, the activity was considerably more as compared to the peptides with one or two disulfide bridges. The peptides enter bacterial and fungal cells rapidly without membrane permeabilization and appear to exert their activity inside the cells rather than at the membrane.
authors.affiliation: CSIR - Centre for Cellular and Molecular Biology, Uppal Road, Hyderabad 500 007, India.
authors.forename: Himanshu
authors.initials: H
authors.lastname: Sharma
authors.forename: Ramakrishnan
authors.initials: R
authors.lastname: Nagaraj
mesh_terms: D000900:Anti-Bacterial Agents / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D000935:Antifungal Agents / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D002176:Candida albicans / Q000187:drug effects*; D004220:Disulfides / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D015195:Drug Design; D006801:Humans; D008826:Microbial Sensitivity Tests; D013329:Structure-Activity Relationship; D023083:beta-Defensins / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D000935:Antifungal Agents; C106641:DEFB4A protein, human; D004220:Disulfides; D023083:beta-Defensins