title: Crystal structure and conformation of a highly constrained linear tetrapeptide Boc-Leu-dehydro Phe-Ala-Leu-OCH3.
abstract: The conformation of a tetrapeptide containing a dehydro amino acid, delta ZPhe, in its sequence has been determined in the crystalline state using X-ray crystallographic techniques. The tetrapeptide, Boc-Leu-delta ZPhe-Ala-Leu-OCH3, crystallizes in the orthorhombic space group P2(1)2(1)2(1) with four molecules in a unit cell of dimensions a = 11.655(1) A, b = 15.698(6) A and c = 18.651(3) A V = 3414.9 A and Dcalc = 1.12 g/cm-3. The asymmetric unit contains one tetrapeptide molecule, C30H46N4O7, a total of 41 nonhydrogen atoms. The structure was determined using the direct methods program SHELXS86 and refined to an R-factor of 0.049 for 3347 reflections (I3.0(I). The linear tetrapeptide in the crystal exhibits a double bend of the Type III-I, with Leu1 (phi = -54.1 degrees, psi = -34.5 degrees) and delta ZPhe2 (phi = -59.9 degrees, psi = -17.1 degrees) as the corner residues of Type III turn and delta ZPhe2 (phi = -59.9 degrees, psi = -17.1 degrees) and Ala3 (phi = -80.4 degrees, psi = 0.5 degrees) residues occupying the corners of Type I turn, with delta ZPhe as the common residue in the double bend. The turn structures are further stabilized by two intramolecular 4----1 type hydrogen bonds.
authors.affiliation: International Centre for Genetic Engineering & Biotechnology, New Delhi, India.
authors.forename: V S
authors.initials: VS
authors.lastname: Chauhan
authors.forename: K K
authors.initials: KK
authors.lastname: Bhandary
mesh_terms: D000595:Amino Acid Sequence; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003460:Crystallization; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009842:Oligopeptides / Q000737:chemistry*; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D009842:Oligopeptides