Conformation of a cyclic decapeptide analog of a repeat pentapeptide sequence of elastin: cyclo‐bis(valyl‐prolyl‐alanyl‐valyl‐glycyl)

Abstract

The conformation of a cyclic decapeptide analog of a repeat sequence of elastin has been determined in the crystalline state using X-ray crystallographic techniques. Tetragonal crystals were grown from a solution of the decapeptide in water; space group P42212, a = 19.439(2) and c = 13.602(1) .ANG., with four formula units (C40H66N10O10.cntdot.4H2O) per unit cell. The cyclic decapeptide in the crystal exhibits exact twofold symmetry. The asymmetric unit contains one pentapeptide and two water molecules for a total of 32 nonhydrogen atoms. The structure has been determined by the application of direct methods and refined by full-matrix least squares to an R index of 0.053 for 2272 reflections with intensities greater than 2.sigma.(I). The backbone conformation of the asymmetric pentapeptide can be described as consisting of a double .beta. bend of Type III-I. The Type III turn has Pro (.vphi. = -59.3.degree.,.psi. = -26.8.degree.) and Ala (.vphi. = 65.9.degree.,.psi. = -23.1.degree.) at the corners while Type I turn has Ala (.vphi. = 65.9.degree.,.psi. = -23.1.degree.) and Val (.vphi. = -98.9.degree.,.psi. = 8.3.degree.) as the corner residues. The cyclic decapeptide has two such double bends linked together by Gly-Val bridges.