Environment- and Sequence-Dependent Modulation of the Double-Stranded to Single-Stranded Conformational Transition of Gramicidin A in Membranes

• DOI: 10.1021/bi980733k
• Publication Date: 2002-07-26T05:19:13Z
• Authors: David Salom; Enrique Pérez-Payá; Jeanick Pascal; Concepción Abad
• Keywords: 0303 health sciences; Cholestenes; Protein Conformation; Circular Dichroism; Phenylalanine; Enterococcus faecium; Lipid Bilayers; Molecular Sequence Data; Gramicidin; Tryptophan; Microbial Sensitivity Tests; 03 medical and health sciences; Spectrometry, Fluorescence; Amino Acid Substitution; Fatty Acids, Unsaturated; Phosphatidylcholines; Amino Acid Sequence; Dimerization; Chromatography, High Pressure Liquid

The role of the membrane lipid composition and the individual Trp residues in the conformational rearrangement of gramicidin A along the folding pathway to its channel conformation has been examined in phospholipid bilayers by means of previously described size-exclusion high-performance liquid chromatography HPLC-based strategy (Bañó et al. (1991) Biochemistry 30, 886). It has been demonstrated that the chemical composition of the membrane influences the transition rate of the peptide rearrangement from double-stranded dimers to beta-helical monomers. The chemical modification of Trp residues, or its substitution by the more hydrophobic residues phenylalanine or naphthylalanine, stabilized the double-stranded dimer conformation in model membranes. This effect was more notable as the number of Trp-substituted residues increased (tetra > tri > di > mono), and it was also influenced by the specific position of the substituted amino acid residue in the sequence, in the order Trp-9 approximately Trp-13 > Trp-11 > Trp-15. Moreover, it was verified that nearly a full contingent of indoles (Trp-13, -11, and -9) is necessary to induce a quantitative conversion from double-stranded dimers to single-stranded monomers, although Trp-9 and Trp-13 seemed to be key residues for the stabilization of the beta-helical monomeric conformation of gramicidin A. The conformation adopted for monomeric Trp --> Phe substitution analogues in lipid vesicles resulted in CD spectra similar to the typical single-stranded beta6.3-helical conformation of gramicidin A. However, the Trp --> Phe substitution analogues showed decreased antibiotic activity as the number of Trp decreased.