Effects of single D-amino acid substitutions on disruption of β-sheet structure and hydrophobicity in cyclic 14-residue antimicrobial peptide analogs related to gramicidin S

D. L. Lee, J. P.S. Powers, K. Pflegerl, M. L. Vasil, R. E.W. Hancock, R. S. Hodges

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Abstract

Gramicidin S (GS) is a 10-residue cyclic β-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 β-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 β-sheet structure on antimicrobial activity.

Original languageEnglish
Pages (from-to)69-84
Number of pages16
JournalJournal of Peptide Research
Volume63
Issue number2
DOIs
Publication statusPublished - Feb 2004
Externally publishedYes

Keywords

  • Antimicrobial peptides
  • Cationic peptides
  • Cyclic peptides
  • D-amino acids
  • Gramicidin S
  • Peptide diastereomers
  • Structure-activity relationship
  • β-sheet

ASJC Scopus subject areas

  • Biochemistry
  • Endocrinology

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