Environment- and sequence-dependent modulation of the double-stranded to single-stranded conformational transition of gramicidin A in membranes.
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.
Departament de Bioquímica i Biologia Molecular, Universitat de València, Burjassot, Spain.
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Salom
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Pérez-Payá
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Pascal
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Abad
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002782:Cholestenes / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D019281:Dimerization; D016984:Enterococcus faecium / Q000187:drug effects / Q000254:growth & development; D005231:Fatty Acids, Unsaturated / Q000737:chemistry; D006096:Gramicidin / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D010649:Phenylalanine / Q000737:chemistry / Q000378:metabolism; D010713:Phosphatidylcholines / Q000737:chemistry; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism
D002782:Cholestenes; D005231:Fatty Acids, Unsaturated; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D006096:Gramicidin; D010649:Phenylalanine; D014364:Tryptophan