title: Tryptophan rotamer distributions in amphipathic peptides at a lipid surface.
abstract: The fluorescence decay of tryptophan is a sensitive indicator of its local environment within a peptide or protein. We describe the use of frequency domain fluorescence spectroscopy to determine the conformational and environmental changes associated with the interaction of single tryptophan amphipathic peptides with a phospholipid surface. The five 18-residue peptides studied are based on a class A amphipathic peptide known to associate with lipid bilayers. The peptides contain a single tryptophan located at positions 2, 3, 7, 12, or 14 in the sequence. In aqueous solution, the peptides are unstructured and a triple-exponential function is required to fit the decay data. Association of the peptides with small unilamellar vesicles composed of egg phosphatidylcholine reduces the complexity of the fluorescence decays to a double exponential function, with a reduced dependence of the preexponential amplitude on peptide sequence. The data are interpreted in terms of a rotamer model in which the modality and relative proportions of the lifetime components are related to the population distribution of tryptophan chi1 rotamers about the Calpha-Cbeta bond. Peptide secondary structure and the disposition of the tryptophan residue relative to the lipid and aqueous phases in the peptide-lipid complex affect the local environment of tryptophan and influence the distribution of side-chain rotamers. The results show that measurement of the temporal decay of tryptophan emission provides a useful adjunct to other biophysical techniques for investigating peptide-lipid and protein-membrane interactions.
authors.affiliation: The Russell Grimwade School of Biochemistry and Molecular Biology, The University of Melbourne, Parkville, Victoria 3052, Australia.
authors.forename: A H
authors.initials: AH
authors.lastname: Clayton
authors.forename: W H
authors.initials: WH
authors.lastname: Sawyer
mesh_terms: D000595:Amino Acid Sequence; D055592:Biophysical Phenomena; D001703:Biophysics; D008051:Lipid Bilayers / Q000737:chemistry*; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013499:Surface Properties; D014364:Tryptophan / Q000737:chemistry*; D014867:Water
chemical_list: D008051:Lipid Bilayers; D010455:Peptides; D010743:Phospholipids; D014867:Water; D014364:Tryptophan