title: The structure of [D-Hyi2,L-Hyi4]meso-valinomycin revealed by X-ray analysis.
abstract: Direct x-ray analysis has been used to determine the crystal structure of [D-Hyi2, L-Hyi4]meso-valinomycin (cyclo[-D-Val-D-Hyi-L-Val-L-Hyi-(D-Val-L-Hyi-L-Val-D-+ ++Hyi)2-], C60H102N6O18), which crystallized from acetone with two solvent molecules. The crystals are trigonal, space group P32, number of molecules per unit cell Z = 3, cell parameters a = b = 15.2085 (8) A, c = 29.3250 (9) A, gamma = 120 degrees. The standard (R) and weighted (Rw) reliability factors after refinement of the atomic coordinates for C, N, and O atoms in the anisotropic thermal motion approximation, allowing for isotropic H atom contributions, were 0.070 and 0.082, respectively. The molecule adopts a distorted bracelet structure which is stabilized by six N-H ... O = C 4----1 type intramolecular hydrogen bonds. The side chains predominantly occupy external pseudoaxial positions relative to the cylindrical axis of the molecule. In contrast to meso-valinomycin, only four of the six Val carbonyl oxygen atoms are directed inwards to form a coordination centre for the molecule, and the carbonyl oxygen atoms of residues D-Val1 and L-Val3 are twisted outward and point away from the centre of the molecule. Although the analogue has a partially formed ion-binding center, it is inaccessible because the hydrophobic isopropyl groups of the D-Hyi2 and L-Hyi4 residues screen the molecular cavity on both sides.
authors.affiliation: Institute of Molecular Genetics, USSR Academy of Sciences, Moscow.
authors.forename: V Z
authors.initials: VZ
authors.lastname: Pletnev
authors.lastname: Mikhailova IYu
authors.forename: V T
authors.initials: VT
authors.lastname: Ivanova
authors.forename: D A
authors.initials: DA
authors.lastname: Langs
authors.forename: P
authors.initials: P
authors.lastname: Grochulski
authors.forename: W L
authors.initials: WL
authors.lastname: Duax
mesh_terms: D000595:Amino Acid Sequence; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D014634:Valinomycin / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D014634:Valinomycin