title: Molecular structures of two crystalline forms of the cyclic heptapeptide antibiotic ternatin, cyclo[-beta-OH-D-Leu-D-Ile-(NMe)Ala-(NMe)Leu-Leu-(NMe)Ala-D-(NMe)Ala-].
abstract: The crystal structures of two solvated forms of ternatin, cyclo[-beta-OH-D-Leu-D-Ile-(NMe)Ala-(NMe)Leu-Leu-(NMe)Ala-D-(NMe)Ala-] are reported. The first crystallizes with two molecules of peptide and one of dioxane in the asymmetric unit: P2(1)2(1)2(1), a = 11.563(1), b = 21.863(2), c = 36.330(4) A. The second crystallizes with two molecules of peptide and one of water in the asymmetric unit: P2(1)2(1)2(1), a = 14.067(2), b = 16.695(1), c = 36.824(6) A. N-Methylation of four of the seven residues of ternatin appears to reduce the number of low-energy conformations the molecule can assume. The same H-bonded macrocyclic ring conformation is adopted by the backbone of each of the four molecules observed here. All the amino-acid side chains, with the exception of D-Ile2, have similar orientations in each of the four conformers. The heptapeptide macrocycle is characterized by: (i) a cis peptide between (NMe)Ala3 and (NMe)Leu4, (ii) a type II beta-bend, involving residues Leu5-(NMe)Ala6-D-(NMe)Ala7-beta-OH-D-Leu1, stabilized by two H-bonds, N1-->O5 and N5-->O1, between Leu5 and beta-OH-D-Leu1 residues, (iii) a third intramolecular H-bond, observed in each of the four molecules, between the hydroxyl group of beta-OH-D-Leu1 and the carbonyl oxygen of D-Ile2.
authors.affiliation: Medical Foundation of Buffalo, Inc., New York.
authors.forename: R
authors.initials: R
authors.lastname: Miller
authors.forename: N M
authors.initials: NM
authors.lastname: Galitsky
authors.forename: W L
authors.initials: WL
authors.lastname: Duax
authors.forename: D A
authors.initials: DA
authors.lastname: Langs
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; D000900:Anti-Bacterial Agents / Q000737:chemistry*; D000935:Antifungal Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D010455:Peptides; D010456:Peptides, Cyclic / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D000935:Antifungal Agents; D009842:Oligopeptides; D010455:Peptides; D010456:Peptides, Cyclic; C085773:ternatin heptapeptide