title: Regularly alternating L,D-peptides. I. The double-stranded left-handed antiparallel beta-helix in the structure of Boc-(L-Val-D-Val)4-OMe.
abstract: The structure of Boc-(L-Val-D-Val)4-OMe has been determined by x-ray single-crystal diffraction analysis. The octapeptide crystallizes in the trigonal system, space group P3(2)21 with a = b = 12.760 A, c = 63.190 A and Z = 6. The independent unit is represented by one octapeptide chain. The structure has been solved by direct methods and it was anisotropically refined by least-squares procedures to a final R value of 0.08 for the 3018 "observed" reflections. One molecule of water was also located in the unit cell. Two octapeptide chains, related by a crystallographic binary axis, wind up around each other giving rise to a double-stranded left-handed antiparallel increases decreases beta 5.6-helix. The dimer, stabilized by 14 interstrand N--H....O = C hydrogen bonds, can be regarded as a cylinder with an hydrophilic inner core represented by the peptide units and an hydrophobic exterior of isopropyl groups. The inner diameter of the cylinder is 5.1 A.
authors.forename: B
authors.initials: B
authors.lastname: Di Blasio
authors.forename: E
authors.initials: E
authors.lastname: Benedetti
authors.forename: V
authors.initials: V
authors.lastname: Pavone
authors.forename: C
authors.initials: C
authors.lastname: Pedone
authors.forename: O
authors.initials: O
authors.lastname: Spiniello
authors.forename: G P
authors.initials: GP
authors.lastname: Lorenzi
mesh_terms: D007536:Isomerism; D008958:Models, Molecular; D009842:Oligopeptides; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D009842:Oligopeptides; C059752:tert-butyloxycarbonylvalyl-valyl-valyl-valyl-valyl-valyl-valyl-valine methyl ester