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Design of Potent, Non‐Toxic Antimicrobial Agents Based Upon the Naturally Occurring Frog Skin Peptides, Ascaphin‐8 and Peptide XT‐7
Author(s) -
Michael Conlon J.,
Galadari Sehamuddin,
Raza Haider,
Condamine Eric
Publication year - 2008
Publication title -
chemical biology and drug design
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.59
H-Index - 77
eISSN - 1747-0285
pISSN - 1747-0277
DOI - 10.1111/j.1747-0285.2008.00671.x
Subject(s) - antimicrobial , candida albicans , peptide , antimicrobial peptides , frog skin , circular dichroism , biochemistry , chemistry , biological activity , amino acid , biology , stereochemistry , microbiology and biotechnology , in vitro , organic chemistry , sodium
The frog skin peptides, ascaphin‐8 (GFKDLLKGAAKALVKTVLF.NH 2 ) and XT‐7 (GLLGPLLKIAAKVGSNLL.NH 2 ), show broad‐spectrum antimicrobial activity but their therapeutic potential is limited by toxicity against mammalian cells. Circular dichroism spectra demonstrate that the peptides adopt an amphipathic α‐helical conformation in a membrane‐mimetic solvent. This study has investigated the cytolytic properties of analogs containing selected amino acid substitutions that increase cationicity while maintaining amphipathicity. Substitutions at Ala 10 , Val 14 , and Leu 18 in ascaphin‐8 by either l ‐Lys or d ‐Lys produced peptides that retained antimicrobial activity against the bacteria Escherichia coli and Staphylococcus aureus and the opportunistic yeast pathogen, Candida albicans but showed appreciably reduced toxicities (>10‐fold) against human erythrocytes, HepG2 hepatoma‐derived cells, and L929 fibroblasts. The improved therapeutic index of the l ‐Lys 18 and d ‐Lys 18 analogs correlated with a decrease in % helicity and in effective hydrophobicity. Substitution of Gly 4 by l ‐Lys in XT‐7 produced an analog with high potency against micro‐organisms (MIC ≤ 25 μ m ) but low cytolytic activity against erythrocytes (LD 50 > 500 μ m ) and this increase in therapeutic index also correlated with decreased helicity and hydrophobicity. Analogs of XT‐7 with increased cationicity, containing multiple substitutions by l ‐Lys, not only displayed increased antimicrobial potencies, particularly against Candida albicans (MIC ≤ 6 μ m ), but also increased hemolytic activities.