title: Electropositive charge in alpha-defensin bactericidal activity: functional effects of Lys-for-Arg substitutions vary with the peptide primary structure.
abstract: Cationic amino acids contribute to alpha-defensin bactericidal activity. Curiously, although Arg and Lys have equivalent electropositive charges at neutral pH, alpha-defensins contain an average of nine Arg residues per Lys residue. To investigate the role of high alpha-defensin Arg content, all Arg residues in mouse Paneth cell alpha-defensin cryptdin 4 (Crp4) and rhesus myeloid alpha-defensin 4 (RMAD-4) were replaced with Lys to prepare (R/K)-Crp4 and (R/K)-RMAD-4, respectively. Lys-for-Arg replacements in Crp4 attenuated bactericidal activity and slowed the kinetics of Escherichia coli ML35 cell permeabilization, and (R/K)-Crp4 required longer exposure times to reduce E. coli cell survival. In marked contrast, Lys substitutions in RMAD-4 improved microbicidal activity against certain bacteria and permeabilized E. coli more effectively. Therefore, Arg-->Lys substitutions attenuated activity in Crp4 but not in RMAD-4, and the functional consequences of Arg-->Lys replacements in alpha-defensins are dependent on the peptide primary structure. In addition, the bactericidal effects of (R/K)-Crp4 and (R/K)-RMAD-4 were more sensitive to inhibition by NaCl than those of the native peptides, suggesting that the high Arg content of alpha-defensins may be under selection to confer superior microbicidal function under physiologic conditions.
authors.affiliation: Department of Pathology & Laboratory Medicine, School of Medicine, University of California, Irvine, CA 92697-4800, USA.
authors.forename: R Alan
authors.initials: RA
authors.lastname: Llenado
authors.forename: Colby S
authors.initials: CS
authors.lastname: Weeks
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Cocco
authors.forename: André J
authors.initials: AJ
authors.lastname: Ouellette
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry*; D001120:Arginine / Q000737:chemistry*; D002463:Cell Membrane Permeability / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects; D008239:Lysine / Q000737:chemistry*; D008253:Macaca mulatta; D051379:Mice; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D023084:alpha-Defensins / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D023084:alpha-Defensins; D001120:Arginine; D008239:Lysine