Crystal structure of achiral nonapeptide Boc-(Aib-DeltaZPhe)4-Aib-OMe at atomic resolution: evidence for a 3(10)-helix.
An x-ray crystallographic analysis was carried out for Boc-(Aib-DeltaZPhe)4-Aib-OMe (1: Boc = t-butoxycarbonyl; Aib = alpha-aminoisobutyric acid; DeltaZPhe = Z-alpha,beta-didehydrophenylalanine) to provide the precise conformational parameters of the octapeptide segment -(Aib-DeltaZPhe)4-. Peptide 1 adopted a typical 3(10)-helical conformation characterized by <phi> = +/-55.8 degrees (50 degrees -65 degrees), <psi> = +/-26.7 degrees (15 degrees -45 degrees), and <omega> = +/-179.5 degrees (168 degrees -188 degrees) for the average values of the -(Aib-DeltaZPhe)4- segment (the range of the eight values). The 3(10)-helix contains 3.1 residues per turn, being close to the "perfect 3(10)-helix" characterized by 3.0 residues per turn. NMR and Fourier transform infrared (FTIR) spectroscopy revealed that the 3(10)-helical conformation at the atomic resolution is essentially maintained in solution. Energy minimization of peptide 1 by semiempirical molecular orbital calculation converged to a 3(10)-helical conformation similar to the x-ray crystallographic 3(10)-helix. The preference for a 3(10)-helix in the -(Aib-DeltaZPhe)4- segment is ascribed to strong inducers of the 3(10)-helix inherent in Aib and DeltaZPhe residues-in particular, the Aib residues tend to stabilize a 3(10)-helix more effectively. Therefore, the -(Aib-DeltaZPhe)4- segment is useful to rationally design an optically inactive 3(10)-helical backbone, which will be of great importance to provide novel insights into noncovalent and covalent chiral interactions of a helical peptide with a chiral molecule.
Department of Environmental Technology and Urban Planning, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan. inai@mse.nitech.ac.jp
Yoshihito
Y
Inai
Tatsuo
T
Oshikawa
Mitsuji
M
Yamashita
Kenichi
K
Tagawa
Tadamichi
T
Hirabayashi
D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D009842:Oligopeptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
D009842:Oligopeptides