title: Effect of aminoisobutyric acid (Aib) substitutions on the antimicrobial and cytolytic activities of the frog skin peptide, temporin-1DRa.
abstract: Temporin-1DRa (HFLGTLVNLAKKIL.NH(2)), first isolated from the skin of the California red-legged frog Rana draytonii, shows broad-spectrum antimicrobial activity but its therapeutic potential is limited by its toxicity against mammalian cells. The cytolytic properties of cationic alpha-helical peptides are determined by a complex interaction between cationicity, hydrophobicity, conformation, and amphipathicity. This study has investigated the cytolytic properties of conformationally constrained analogs of temporin-1DRa containing alpha-aminoisobutyric acid (Aib) substitutions. Cytolytic activity was determined against the bacteria Escherichia coli and Staphylococcus aureus, the opportunistic yeast pathogen, Candida albicans, human erythrocytes, HepG2 hepatoma-derived cells, and L929 fibroblasts. Aib substitutions at Gly(4), Asn(8), and Ala(10) increased both % helicity, determined in methanol solution, and hydrophobicity resulting in increases in both antimicrobial potencies and toxicities against the mammalian cells. Substitution at Leu(6) resulted in an appreciable decrease in cytolytic activity against all cells whereas the substitutions at His(1), Phe(2), Leu(3), Thr(5), and Val(7) had only minor effects on activity. Substitutions at Leu(9), Ile(13), Leu(14) produced analogs with decreased helicity and hydrophobicity that retained activity against microorganisms but showed appreciably lower cytolytic activities against mammalian cells. In particular, the fourfold increase in therapeutic index [ratio of LC(50) against erythrocytes to minimum inhibitory concentration (MIC) against microorganisms] of [Aib(13)]temporin-1DRa identifies it as a compound with potential for development as a therapeutically valuable anti-infective agent.
authors.affiliation: Department of Biochemistry, Faculty of Medicine and Health Sciences, United Arab Emirates University, 17666 Al-Ain, United Arab Emirates. jmconlon@uaeu.ac.ae
authors.forename: J Michael
authors.initials: JM
authors.lastname: Conlon
authors.forename: Rokaya
authors.initials: R
authors.lastname: Al-Kharrge
authors.forename: Eman
authors.initials: E
authors.lastname: Ahmed
authors.forename: Haider
authors.initials: H
authors.lastname: Raza
authors.forename: Sehamuddin
authors.initials: S
authors.lastname: Galadari
authors.forename: Eric
authors.initials: E
authors.lastname: Condamine
mesh_terms: D000621:Aminoisobutyric Acids / Q000737:chemistry*; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002942:Circular Dichroism; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D008826:Microbial Sensitivity Tests; D011487:Protein Conformation; D011898:Ranidae
chemical_list: D000621:Aminoisobutyric Acids; D023181:Antimicrobial Cationic Peptides; C524205:temporin 1DRa, Rana draytonii