Conformation of cyclic octapeptides. VI. Structure of cyclo-bis-(-L-alanyl-glycyl-L-prolyl-L-phenylalanyl-) tetrahydrate.
C38H48N8O8.4H2O, Mr = 816.9, monoclinic, P21, a = 10.381 (1), b = 13.273 (1), c = 15.742 (1) A. beta = 101.83 (1) degree, V = 2123.1 A3, Z = 2, Dx = 1.278 g cm-3, lambda (Cu K alpha) = 1.5418 A, mu = 7.6 cm-1, F(000) = 872, R = 0.035, wR = 0.045 for 3497 reflections [I greater than 2 sigma (I)], 4552 unique reflections measured. The synthetic cyclic octapeptide crystallizes from water/methanol solution as a tetrahydrate and the crystals are isomorphous to those of the disulfide-bridged cystine analog cyclo-bis(-L-Cys-Gly-L-Pro-L-Phe-) [Kopple, Wang, Cheng & Bhandary (1988). J. Am. Chem. Soc. 110, 4168-4176]. The coordinates of the Cys analog were taken as the starting coordinates for full-matrix least-squares refinement. The cyclic octapeptide ring has two beta turns encompassing the residues Pro-L-Phe, one type I and the other type II, with all peptide links trans. The conformation of the cyclic octapeptide backbone is similar to the Cys analog; all backbone dihedral angles in the two molecules agree to within 6 degrees. This suggests that the disulfide bridge of the Cys analog does not impose any conformational constraint on the octapeptide ring backbone.
Oral Biology Department, School of Dental Medicine, University at Buffalo, New York 14214.
K K
KK
Bhandary
K D
KD
Kopple
D000595:Amino Acid Sequence; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000737:chemistry*; D011487:Protein Conformation; D014961:X-Ray Diffraction
D010456:Peptides, Cyclic; C071633:cyclo-bis(alanyl-glycyl-prolyl-phenylalanyl)