title: Three complete turns of a 3(10)-helix at atomic resolution: the crystal structure of Z-(Aib)11-OtBu.
abstract: The crystal structure of the synthetic protected oligopeptide Z-(Aib)11-OtBu was determined by x-ray crystallography. The undecapeptide folds in a regular 3(10)-helix with nine consecutive 4 --> 1 hydrogen bonds. At present, this is the largest available structure of a homopeptide (including homopeptides consisting of standard amino acids) and also the longest observed regular 3(10)-helix at atomic resolution. Z-(Aib)11-OtBu crystallizes readily from hot ethanol-water mixture and is one of the crystals in which no solvent molecule is co-crystallized. In the crystal head-to-tail hydrogen bonded columns are formed in the [1 0 1] direction. Each helical column is surrounded by six others, whereby two are packed in parallel and four in antiparallel fashion. Helical columns are packed via apolar crystal contacts. The crystal structure of Z-(Aib)11-OtBu is compared with the crystal structures of Z-(Aib)10-OtBu and Z-(Aib)9-OtBu. The similarities and differences are analysed.
authors.affiliation: Institute of Molecular Biology and Biotechnology (IMBB), FORTH, PO Box 1527, 71110 Heraklion, Greece. rege777@yahoo.com
authors.forename: Renate
authors.initials: R
authors.lastname: Gessmann
authors.forename: Hans
authors.initials: H
authors.lastname: Brückner
authors.forename: Kyriacos
authors.initials: K
authors.lastname: Petratos
mesh_terms: D000621:Aminoisobutyric Acids / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D009842:Oligopeptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D000621:Aminoisobutyric Acids; D009842:Oligopeptides