title: Helical distortion in tryptophan- and lysine-anchored membrane-spanning alpha-helices as a function of hydrophobic mismatch: a solid-state deuterium NMR investigation using the geometric analysis of labeled alanines method.
abstract: We used solid-state deuterium NMR spectroscopy and geometric analysis of labeled alanines to investigate the structure and orientation of a designed synthetic hydrophobic, membrane-spanning alpha-helical peptide that is anchored within phosphatidylcholine (PC) bilayers using both Trp and Lys side chains near the membrane/water interface. The 23-amino-acid peptide consists of an alternating Leu/Ala core sequence that is expected to be alpha-helical, flanked by aromatic and then cationic anchors at both ends of the peptide: acetyl-GKALW(LA)(6)LWLAKA-amide (KWALP23). The geometric analysis of labeled alanines method was elaborated to permit the incorporation and assignment of multiple alanine labels within a single synthetic peptide. Peptides were incorporated into oriented bilayers of dilauroyl- (di-C12:0-), dimyristoyl- (di-C14:0-), or dioleoyl- (di-C18:1c-) PC. In the C12:0 and C14:0 lipids, the (2)H-NMR quadrupolar splittings for the set of six core alanines could not be fit to a canonical undistorted alpha-helix. Rather, we found that a model containing a helical distortion, such as a localized discontinuity or "kink" near the peptide and bilayer center, could fit the data for KWALP23 in these shorter lipids. The suggestion of helix distortion was confirmed by (2)H-NMR spectra for KWALP23 in which Leu(8) was changed to deuterated Ala(8). Further analysis involving reexamination of earlier data led to a similar conclusion that acetyl-GWW(LA)(8)LWWA-amide (WALP23) is distorted in dilauroyl-PC, allowing significant improvement in the fitting of the (2)H-NMR results. In contrast, WALP23 and KWALP23 are well represented as undistorted alpha-helices in dioleoyl-PC, suggesting that the distortion could be a response to hydrophobic mismatch between peptide and lipids.
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA.
authors.forename: Anna E
authors.initials: AE
authors.lastname: Daily
authors.forename: Denise V
authors.initials: DV
authors.lastname: Greathouse
authors.forename: Patrick C A
authors.initials: PC
authors.lastname: van der Wel
authors.forename: Roger E
authors.initials: RE
authors.lastname: Koeppe
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D003903:Deuterium; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry*; D050356:Lipid Metabolism; D008239:Lysine / Q000737:chemistry*; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry; D017433:Protein Structure, Secondary; D013194:Staining and Labeling / Q000379:methods*; D014364:Tryptophan / Q000737:chemistry*