Observation of a mixed antiparallel and parallel beta-sheet motif in the crystal structure of Boc-Ala-Ile-Aib-OMe.
A diastereomeric mixture of the tripeptide Boc-Ala-Ile-Aib-OMe crystallized in the space group P1 from CH3OH/H2O. The unit cell parameters are a = 10.593(2) A, b = 14.377(3) A, c = 17.872(4) A, alpha = 104.41(2) degrees, beta = 90.55(2) degrees, gamma = 106.91(2) degrees, V = 2512.4 A3, Z = 4. X-Ray crystallographic studies show the presence of four molecules in the asymmetric unit consisting of two pairs of diastereomeric peptides, Boc-L-Ala-L-Ile-Aib-OMe and Boc-L-Ala-D-Ile-Aib-OMe. The four molecules in the asymmetric unit form a rarely found mixed antiparallel and parallel beta-sheet hydrogen bond motif. The Ala and (L,D)-Ile residues in all the four molecules adopt the extended conformations, while the phi, psi values of the Aib residues are in the right-handed helical region. In one of the molecules the Ile sidechain adopts the unusual gauche conformation about the C beta-C gamma bond.
Department of Physics, Indian Institute of Science, Bangalore, India.
S
S
Datta
N
N
Shamala
R
R
Gurunath
P
P
Balaram
D003460:Crystallization; D018360:Crystallography, X-Ray; D009842:Oligopeptides / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding
D009842:Oligopeptides; D010455:Peptides; C103565:t-butyloxycarbonyl-alanyl-isoleucyl-aminoisobutyrate methyl ester