Effects of single D-amino acid substitutions on disruption of beta-sheet structure and hydrophobicity in cyclic 14-residue antimicrobial peptide analogs related to gramicidin S.
Gramicidin S (GS) is a 10-residue cyclic beta-sheet peptide with lytic activity against the membranes of both microbial and human cells, i.e. it possesses little to no biologic specificity for either cell type. Structure-activity studies of de novo-designed 14-residue cyclic peptides based on GS have previously shown that higher specificity against microbial membranes, i.e. a high therapeutic index (TI), can be achieved by the replacement of a single L-amino acid with its corresponding D-enantiomer [Kondejewski, L.H. et al. (1999) J. Biol. Chem. 274, 13181]. The diastereomer with a D-Lys substituted at position 4 caused the greatest improvement in specificity vs. other L to D substitutions within the cyclic 14-residue peptide GS14, through a combination of decreased peptide amphipathicity and disrupted beta-sheet structure in aqueous conditions [McInnes, C. et al. (2000) J. Biol. Chem. 275, 14287]. Based on this information, we have created a series of peptide diastereomers substituted only at position 4 by a D- or L-amino acid (Leu, Phe, Tyr, Asn, Lys, and achiral Gly). The amino acids chosen in this study represent a range of hydrophobicities/hydrophilicities as a subset of the 20 naturally occurring amino acids. While the D- and L-substitutions of Leu, Phe, and Tyr all resulted in strong hemolytic activity, the substitutions of hydrophilic D-amino acids D-Lys and D-Asn in GS14 at position 4 resulted in weaker hemolytic activity than in the L-diastereomers, which demonstrated strong hemolysis. All of the L-substitutions also resulted in poor antimicrobial activity and an extremely low TI, while the antimicrobial activity of the D-substituted peptides tended to improve based on the hydrophilicity of the residue. D-Lys was the most polar and most efficacious substitution, resulting in the highest TI. Interestingly, the hydrophobic D-amino acid substitutions had superior antimicrobial activity vs. the L-enantiomers although substitution of a hydrophobic D-amino acid increases the nonpolar face hydrophobicity. These results further support the role of hydrophobicity of the nonpolar face as a major influence on microbial specificity, but also highlights the importance of a disrupted beta-sheet structure on antimicrobial activity.
Lee
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Department of Biochemistry, University of Alberta, Edmonton T6G 2H7, Canada.
Powers
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JP
Pflegerl
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Vasil
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Hancock
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Hodges
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D015057:1-Naphthylamine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D019943:Amino Acid Substitution; D000890:Anti-Infective Agents / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D052160:Benzothiazoles; D002176:Candida albicans / Q000187:drug effects; D002232:Carbocyanines / Q000737:chemistry / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D002942:Circular Dichroism; D005998:Glycine / Q000737:chemistry; D006090:Gram-Negative Bacteria / Q000187:drug effects; D006094:Gram-Positive Bacteria / Q000187:drug effects; D006096:Gramicidin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008564:Membrane Potentials / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D015003:Yeasts / Q000187:drug effects
D000890:Anti-Infective Agents; D052160:Benzothiazoles; D002232:Carbocyanines; D010456:Peptides, Cyclic; D006096:Gramicidin; C012944:3,3'-dipropyl-2,2'-thiadicarbocyanine; C005444:N-phenyl-1-naphthylamine; D015057:1-Naphthylamine; D005998:Glycine