title: Membranolytic selectivity of cystine-stabilized cyclic protegrins.
abstract: To correlate conformational rigidity with membranolytic selectivity of antimicrobial activity and cytotoxicity, we prepared six cyclic analogs of protegrin-1 (PG-1), an 18-residue cationic peptide with a broad-spectrum antimicrobial activity. These cyclic protegrins bear end-to-end peptide bonds together with varying numbers (zero to three) of cross-strand disulfide constraints. The most constrained analog is a cyclic tricystine protegrin (ccPG 3) containing three evenly spaced, parallel disulfide bonds. Antimicrobial assays against 10 organisms in low- and high-salt conditions showed that these cyclic protegrins were broadly active with different antimicrobial profiles against Gram-positive and Gram-negative bacteria, fungi and one tested virus, HIV-1. Compared to PG-1, the cyclic tricystine ccPG 3 displayed approximately a 10-fold decrease in hemolytic activity against human cells and 6- to 30-fold improvement of membranolytic selectivity against six of the 10 tested organisms. In contrast, [DeltaSS]cPG 8, a cyclic protegrin with no disulfide bond, and [DeltaCys6,15]cPG 5, a cyclic mimic of PG-1 with one disulfide bond, exhibited activity spectra, potency, and cytotoxicity similar to PG-1. Circular dichroism showed that cyclic protegrins containing with one to three cystine bonds displayed some degree of beta-strand structures in water/trifluoroethanol or phosphate-buffered solutions. Collectively, our results indicate that cyclic structures are useful in the design of antimicrobial peptides and that an increase in the conformational rigidity of protegrins may confer membranolytic selectivity that dissociates antimicrobial activity from hemolytic activity.
authors.affiliation: Vanderbilt University, Department of Microbiology and Immunology, Nashville, TN 37232, USA. james.tam@mcmail.vanderbilt.edu
authors.forename: J P
authors.initials: JP
authors.lastname: Tam
authors.forename: C
authors.initials: C
authors.lastname: Wu
authors.forename: J L
authors.initials: JL
authors.lastname: Yang
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000900:Anti-Bacterial Agents; D019380:Anti-HIV Agents / Q000737:chemistry / Q000494:pharmacology; D000890:Anti-Infective Agents / Q000737:chemistry* / Q000494:pharmacology; D000935:Antifungal Agents / Q000737:chemistry / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides; D002175:Candida / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects; D002942:Circular Dichroism; D003553:Cystine / Q000737:chemistry*; D004910:Erythrocyte Membrane / Q000187:drug effects; D006090:Gram-Negative Bacteria / Q000187:drug effects; D006094:Gram-Positive Bacteria / Q000187:drug effects; D015497:HIV-1 / Q000187:drug effects; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000737:chemistry / Q000494:pharmacology; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry* / Q000494:pharmacology; D012996:Solutions; D012997:Solvents; D013329:Structure-Activity Relationship; D014270:Trifluoroethanol; D014867:Water
chemical_list: D000900:Anti-Bacterial Agents; D019380:Anti-HIV Agents; D000890:Anti-Infective Agents; D000935:Antifungal Agents; D023181:Antimicrobial Cationic Peptides; D010456:Peptides, Cyclic; D011506:Proteins; D012996:Solutions; D012997:Solvents; C094880:protegrin-1; D014867:Water; D003553:Cystine; D014270:Trifluoroethanol