title: Molecular structure of cyclo[-(D-Val-L-Hyi-L-Val-D-Hyi)2-] revealed by x-ray analysis.
abstract: The crystal structure of a synthetic analogue of valinomycin, cyclo[-(D-Val-L-Hyi-L-Val-D-Hyi)2-] (octa-meso-valinomycin) (I) (C40H68N4O12.1.5.C4H8O2, M(r) = 937.01 + 88.10), has been determined. Crystals grown from dioxane are monoclinic, space group P2(1)/a, with cell parameters a = 21.487 (8), b = 16.836 (5), c = 16.089 (4) A, beta = 111.70 (4), and Z = 4. The atomic coordinates for nonhydrogen atoms were refined in the anisotropic thermal motion approximation. H atom positions were included in the structure factor calculations at their geometrically expected positions. Values of the standard and weighted R factors after refinement are 0.11 and 0.13, respectively. The conformation of the depsipeptide crystallized from dioxane is different from that crystallized from chloroform (II). The molecule adopts a rectangular shape with two type IV beta-turns containing a hydrogen bond and possesses pseudorotational symmetry. The side chains are located on the molecular periphery. The orientation of the carbonyl groups of the molecule is not conducive for efficient metal-ion coordination and in the observed conformation cannot behave as an ionophore. In the crystal the molecules form infinite chains parallel to the c axis, and are stabilized by two intermolecular hydrogen bonds that are shorter and have better geometry than the intramolecular hydrogen bonds. A phi/psi plot for dodecadepsipeptides with a (DLLD)3 sequence has well-defined areas for Val and Hyi residues only in cases when the crystals have been grown from nonpolar or medium-polar solvents. The phi/psi plot for octadepsipeptides crystallized from chloroform (II) shows this behavior also.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Medical Foundation of Buffalo, Inc., New York.
authors.forename: P
authors.initials: P
authors.lastname: Grochulski
authors.forename: G D
authors.initials: GD
authors.lastname: Smith
authors.forename: D A
authors.initials: DA
authors.lastname: Langs
authors.forename: W L
authors.initials: WL
authors.lastname: Duax
authors.forename: V Z
authors.initials: VZ
authors.lastname: Pletnev
authors.forename: V T
authors.initials: VT
authors.lastname: Ivanov
mesh_terms: D000595:Amino Acid Sequence; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation; D014634:Valinomycin / Q000031:analogs & derivatives* / Q000737:chemistry; D014961:X-Ray Diffraction / Q000379:methods
chemical_list: D010456:Peptides, Cyclic; C077027:octa-valinomycin; D014634:Valinomycin