title: The (i, i + 4) Phe-His interaction studied in an alanine-based alpha-helix.
abstract: Two models have been considered for the helix-stabilizing Phe-His+ interaction in C-peptide: (1) the H-bond model in which His+ acts as an H-bond donor and the aromatic ring of Phe acts as an acceptor, and (2) a helix dipole model, in which Phe constrains His so that there is a stronger interaction between His+ and the helix dipole. To decide between these models, we compared the effect on helix stability of the Phe-His interaction near the middle versus close to the C terminus of an alanine-based peptide. The nature of the interaction is the same at either position, in agreement with the H-bond model. The results show further that a weak helix-stabilizing Phe-His interaction can be detected when His is uncharged. Replacement of Phe by the saturated analog Cha (beta-cyclohexylalanine) gives no interaction, as predicted by the H-bond model.
authors.affiliation: Department of Biochemistry, Stanford University Medical School, CA 94305-5307.
authors.forename: K M
authors.initials: KM
authors.lastname: Armstrong
authors.forename: R
authors.initials: R
authors.lastname: Fairman
authors.forename: R L
authors.initials: RL
authors.lastname: Baldwin
mesh_terms: D000409:Alanine / Q000737:chemistry; D000595:Amino Acid Sequence; D002942:Circular Dichroism; D006639:Histidine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D010649:Phenylalanine / Q000031:analogs & derivatives / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D010455:Peptides; C028544:cyclohexylalanine; D010649:Phenylalanine; D006639:Histidine; D000409:Alanine