title: Large-scale synthesis and functional elements for the antimicrobial activity of defensins.
abstract: Human neutrophil defensins, and their analogues incorporating anionic, hydrophobic or cationic residues at the N- and C-termini, were synthesized by solid-phase procedures. The synthetic defensins were examined for their microbicidal activity against Candida albicans, two Gram-negative bacteria (Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis) and two Gram-positive bacteria (Streptococcus gordonii and Streptococcus mutans). The human neutrophil peptide 1 (HNP1) and HNP2 were found to be potent candidacidal agents. HNP3, which differs by one amino acid at the N-terminus of its sequence, was totally inactive. The Gram-negative bacteria A. actinomycetemcomitans and P. gingivalis and the Gram-positive bacteria S. gordonii and S. mutans were insensitive to human defensins. However, the insertion of two basic residues, such as arginine, at both the N-terminus and the C-terminus of HNP2 significantly enhanced antifungal and antibacterial activity. The addition of anionic residues, such as aspartic acid, at the N- and C-termini rendered the molecule totally inactive. The presence of two hydrophobic amino acids, such as valine, at the N-terminus of HNP2 and of two basic arginine residues at its C-terminus resulted in molecules that were optimally active against these oral pathogens. The results suggest that the N- and C-terminal residues in defensin peptides are the crucial functional elements that determine their microbicidal potency. The three-dimensional structure of all defensins constitutes the same amphiphilic beta-sheet structure, with the polar face formed by the N- and C-terminal residues playing an important role in defining microbicidal potency and the antimicrobial spectrum. The enhanced microbicidal activity observed for defensin peptides with two basic residues at both the N- and C-termini could be due to optimization of the amphiphilicity of the structure, which could facilitate specific interactions with the microbial membranes.
authors.affiliation: Division of Periodontics, School of Dentistry, Marquette University, 570 North 16th Street, Milwaukee, WI 53201, USA. Periathambya@vms.csd.mu.edu
authors.forename: P A
authors.initials: PA
authors.lastname: Raj
authors.forename: K J
authors.initials: KJ
authors.lastname: Antonyraj
authors.forename: T
authors.initials: T
authors.lastname: Karunakaran
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000166:cytology / Q000187:drug effects; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D000935:Antifungal Agents / Q000138:chemical synthesis / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology; D002176:Candida albicans / Q000166:cytology / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D023082:Defensins; D004220:Disulfides / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009504:Neutrophils; D016966:Porphyromonas gingivalis / Q000166:cytology / Q000187:drug effects; D017433:Protein Structure, Secondary; D011506:Proteins / Q000138:chemical synthesis* / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D011817:Rabbits; D055672:Static Electricity; D013291:Streptococcus / Q000166:cytology / Q000187:drug effects; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D023084:alpha-Defensins
chemical_list: D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D000935:Antifungal Agents; D023082:Defensins; D004220:Disulfides; D011506:Proteins; D023084:alpha-Defensins; C406413:human neutrophil peptide 1; C406416:human neutrophil peptide 2; C406427:human neutrophil peptide 3