Antimicrobial properties of the frog skin peptide, ranatuerin-1 and its [Lys-8]-substituted analog.
The predicted conformation of ranatuerin-1 (SMLSVLKNLG(10)KVGLGFVACK(20)INK QC), an antimicrobial peptide first isolated from the skin of the bullfrog Rana catesbeiana, comprises three structural domains: alpha-helix (residues 1-8), beta-sheet (residues 11-16) and beta-turn (residues 20-25). Circular dichroism studies confirm significant alpha-helical character in 50% trifluoroethanol. Replacement of Cys-19 and Cys-25 by serine resulted only in decreased antimicrobial potency but deletion of either the cyclic heptapeptide region [residues (19-25)] or the N-terminal domain [residues (1-8)] produced inactive analogs. Substitution of the glycine residues in the central domain of the [Ser-19, Ser-25] analog by lysine produced inactive peptides despite increased alpha-helical content and cationicity. The substitution Asn-8-->Lys gave a ranatuerin-1 analog with increased alpha-helicity and cationicity and increased potency against a range of Gram-positive and Gram-negative bacteria and against C. albicans but only a small increase (21%) in hemolytic activity. In contrast, increasing alpha-helicity and hydrophobicity by the substitution Asn-22-->Ala resulted in a 3.5-fold increase in hemolytic activity. Effects on antimicrobial potencies of substitutions of neutral amino acids at positions 4, 18, 22, and 24 by lysine were less marked. Strains of pathogenic E. coli from different groups showed varying degrees of sensitivity to ranatuerin-1 (MIC between 5 and 40 microM) but [Lys-8] ranatuerin-1 showed increased potency (between 2- and 8-fold; P < 0.01) against all strains. The data demonstrate that [Lys-8] ranatuerin-1 shows potential as a candidate for drug development.
Department of Medical Microbiology, Faculty of Medicine and Health Sciences, United Arab Emirates University, P.O. Box 17666, Al-Ain, United Arab Emirates.
Agnes
A
Sonnevend
Floyd C
FC
Knoop
Mahrendra
M
Patel
Tibor
T
Pál
Ana Maria
AM
Soto
J Michael
JM
Conlon
D019943:Amino Acid Substitution; D029845:Amphibian Proteins; D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D023181:Antimicrobial Cationic Peptides; D002942:Circular Dichroism; D008239:Lysine / Q000737:chemistry*; D008826:Microbial Sensitivity Tests; D010455:Peptides; D011506:Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000494:pharmacology*; D011892:Rana catesbeiana / Q000033:anatomy & histology* / Q000378:metabolism; D012867:Skin / Q000737:chemistry*; D013329:Structure-Activity Relationship
D029845:Amphibian Proteins; D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D010455:Peptides; D011506:Proteins; C121230:ranatuerin; D008239:Lysine