title: A study of alpha-helix hydration in polypeptides, proteins, and viruses using vibrational raman optical activity.
abstract: A vibrational Raman optical activity (ROA) study, supplemented by protein X-ray crystal structure data, of alpha-helices in polypeptides, proteins, and viruses has suggested that ROA bands in the extended amide III spectral region may be used to distinguish between two types of right-handed alpha-helix. One type, associated with a positive ROA band at approximately 1300 cm(-1), dominates in hydrophobic environments and appears to be unhydrated; the other, associated with a positive ROA band at approximately 1340 cm(-1), dominates in hydrophilic environments and appears to be hydrated. Evidence is presented to support the hypothesis that unhydrated alpha-helix corresponds to the canonical conformation alpha(c) and hydrated alpha-helix to a more open conformation alpha(o) stabilized by hydrogen bonding of a water molecule or a hydrophilic side chain to the peptide carbonyl. Alpha-helical poly(L-lysine) and poly(L-ornithine) in aqueous solution and poly(L-alanine) in dichloracetic acid display both bands, but alpha-helical poly(l-glutamic acid) in aqueous solution and poly(gamma-benzyl L-glutamate) in CHCl(3) display only the approximately 1340 cm(-1) band and so may exist purely as alpha(o) due to enhanced stabilization of this conformation by particular side chain characteristics. The ROA spectrum of poly(beta-benzyl L-aspartate) in CHCl(3) reveals that it exists in a single left-handed alpha-helical state more analogous to alpha(o) than to alpha(c).
authors.affiliation: Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom.
authors.forename: Iain H
authors.initials: IH
authors.lastname: McColl
authors.forename: Ewan W
authors.initials: EW
authors.lastname: Blanch
authors.forename: Lutz
authors.initials: L
authors.lastname: Hecht
authors.forename: Laurence D
authors.initials: LD
authors.lastname: Barron
mesh_terms: D017912:Inovirus / Q000737:chemistry*; D007768:Lactalbumin / Q000737:chemistry*; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013059:Spectrum Analysis, Raman; D014867:Water / Q000737:chemistry
chemical_list: D010455:Peptides; D014867:Water; D007768:Lactalbumin; D009113:Muramidase