title: Ion-pair and charged hydrogen-bond interactions between histidine and aspartate in a peptide helix.
abstract: The effect on helix stability of placing a single pair of His-Asp or Asp-His residues, spaced (i, i + 3), (i, i + 4), or (i, i + 5), in an alanine-based peptide has been determined. The peptides have identical amino acid compositions, intrinsic helix propensities, and closely similar charge-helix dipole interactions, but they have different side chain interactions. Their helix contents are measured by circular dichroism over the pH range of 2-9, and the strength of a particular side chain interaction is determined from the increase in helix content over the reference peptide with the (i, i + 5) spacing. Side chain interactions are found for both the (i, i + 3) and (i, i + 4) spacings but only in the His-Asp orientation. Charged hydrogen-bond interactions occur at extreme pH values, and they are almost as strong as the ion-pair interactions at pH 5.5; but only the (i, i + 4) His-Asp peptide forms a strong hydrogen bond at pH 2, and only the (i, i + 3) peptide forms a strong hydrogen bond at pH 8.5. The ion-pair interactions are not screened effectively by 1 M NaCl, and hydrogen bonds probably account for most of their strength.
authors.affiliation: Department of Biochemistry, Beckman Center, Stanford Medical Center, California 94305-5307, USA.
authors.forename: B M
authors.initials: BM
authors.lastname: Huyghues-Despointes
authors.forename: R L
authors.initials: RL
authors.lastname: Baldwin
mesh_terms: D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000737:chemistry* / Q000378:metabolism; D006639:Histidine / Q000737:chemistry* / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D017510:Protein Folding
chemical_list: D010455:Peptides; D001224:Aspartic Acid; D006639:Histidine; D006859:Hydrogen