title: An unusual C-H...O hydrogen bond mediated reversal of polypeptide chain direction in a synthetic peptide helix.
abstract: An unusual C-terminal conformation has been detected in a synthetic decapeptide designed to analyze the stereochemistry of helix termination in polypeptides. The crystal structure of the decapeptide Boc-Leu-Aib-Val-Ala-Leu-Aib-Val-(D)Ala-(D)Leu-Aib-OMe reveals a helical segment spanning residues 1-7 and helix termination by formation of a Schellman motif, generated by (D)Ala(8) adopting the left-handed helical (alpha(L)) conformation. The extended conformation at (D)Leu(9) results in a compact folded structure, stabilized by a potentially strong C-H. O hydrogen bond between Ala(4) C(alpha)H and (D)Leu(9) CO. The parameters for C-H. O interaction are Ala(4) C(alpha)H. O=C (D)Leu(9) distance 3.27 A, C(alpha)-H. O angle 176 degrees, and O. H(alpha) distance 2.29 A. This structure suggests that insertion of contiguous D-residues may provide a handle for the generation of designed structures containing more than one helical segment folded in a compact manner.
authors.affiliation: Department of Physics, Indian Institute of Science, Bangalore-, 560012, India.
authors.forename: S
authors.initials: S
authors.lastname: Aravinda
authors.forename: N
authors.initials: N
authors.lastname: Shamala
authors.forename: A
authors.initials: A
authors.lastname: Pramanik
authors.forename: C
authors.initials: C
authors.lastname: Das
authors.forename: P
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000595:Amino Acid Sequence; D006860:Hydrogen Bonding; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D010455:Peptides