Proton magnetic resonance and conformational energy calculations of repeat peptides of tropoelastin: the pentapeptide

Abstract

The detailed conformation of a repeating pentapeptide segment, HCO-L-Val₁-L-Pro₂-Gly₃-L-Val₄-Gly₅-OMe, of tropoelastin has been investigated using theoretical conformational energy calculations and ¹H n.m.r. studies in CDCl₃. Theoretical conformational energy calculations suggest the existence of two broad classes of conformations. One class of conformations (A) is stabilized by a Type II β-turn, involving the Val₄ NH and the Val₁ CO, a 14-membered hydrogen bonded ring between the Val₁ NH and the Val₄ CO, and an 11-membered hydrogen bonded system, called a γ-turn, between the Gly₃ NH and the Gly₅ CO. The second class of conformations (B) is stabilized by the same Type II β-turn and 11-membered hydrogen bonded ring and by a seven-membered hydrogen bonded ring between the Gly₅ NH and the Gly₃ CO. The theoretical results correlate reasonably well with torsion angles derived from ³J_C^αH–NH coupling constants obtained in the ¹H n.m.r. studies. Temperature dependence and solvent perturbation of NH proton chemical shifts support the above intramolecular hydrogen bonds.