STUDIES ON THE CONFORMATION AND INTERACTIONS OF ELASTIN: NUCLEAR MAGNETIC RESONANCE OF THE POLYHEXAPEPTIDE

Abstract
Synthesis, proton magnetic resonance and carbon-13 magnetic resonance characterizations, including complete assignments, are reported for the polyhexapeptide of elastin, HCO-Val-(Ala1-Pro2-Gly3-Val4-Gly5-Val6)18-OMe. Temperature dependence of peptide NH chemical shifts and solvent dependence of peptide C-O chemical shifts have been determined in several solvents and have been interpreted in terms of four hydrogen bonded rings for each repeat of the polyhexapeptide. The more stable hydrogen bonded ring is a β-turn involving Ala1 C-O…HN·Val4 More dynamic hydrogen bonds are an 11-atom hydrogen bonded ring Gly3 NH · O-C Gly5, a 7-atom hydrogen bonded ring (a γ-turn) Gly3 C-O … HN · Gly5 and a 23-atom hydrogen bonded ring Val61NH … O-C Val6(l+l). This set of hydrogen bonds results in a right-handed β-spiral structure with slightly more than two repeats (approximately 2.2) per turn of spiral. The β-spiral structure is briefly discussed relative to data on the elastic fiber.