title: Critical main-chain length for conformational conversion from 3(10)-helix to alpha-helix in polypeptides.
abstract: To assess the minimal peptide length required for the stabilization of the alpha-helix relative to the 3(10)-helix in Aib-rich peptides, we have solved the X-ray diffraction structures of the terminally blocked sequential hexa- and octapeptides with the general formula-(Aib-L-Ala)n-(n = 3 and 4, respectively). The hexapeptide molecules are completely 3(10)-helical with four 1----4 intramolecular N-H . . . O = C H-bonds. On the other hand, the octapeptide molecules are essentially alpha-helical with four 1----5 H-bonds; however, the helix is elongated at the N-terminus, with two 1----4 H-bonds, giving these molecules a mixed alpha/3(10)-helical character. In both compounds the right-handed screw sense of the helix is dictated by the presence of the Ala residues of L-configuration. This study represents the first experimental proof for a 3(10)----alpha-helix conversion in the crystal state induced by peptide backbone lengthening only.
authors.affiliation: Department of Chemistry, University of Naples, Italy.
authors.forename: V
authors.initials: V
authors.lastname: Pavone
authors.forename: E
authors.initials: E
authors.lastname: Benedetti
authors.forename: B
authors.initials: B
authors.lastname: Di Blasio
authors.forename: C
authors.initials: C
authors.lastname: Pedone
authors.forename: A
authors.initials: A
authors.lastname: Santini
authors.forename: A
authors.initials: A
authors.lastname: Bavoso
authors.forename: C
authors.initials: C
authors.lastname: Toniolo
authors.forename: M
authors.initials: M
authors.lastname: Crisma
authors.forename: L
authors.initials: L
authors.lastname: Sartore
mesh_terms: D055598:Chemical Phenomena; D002627:Chemistry, Physical; D006860:Hydrogen Bonding; D015394:Molecular Structure; D010455:Peptides; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D010455:Peptides