Calculation of dipole moment changes due to peptide librations in the dynamic β-spiral of the polypentapeptide of elastin

Abstract

It has been proposed that the polypentapeptide of elastin, (L·Val1-L·Pro2-Gly3-L·Val4-Gly5)n, on increasing temperature in water, develops a dynamic β-spiral conformation within which occurs a Val4-Gly5-Val1 suspended segment capable of large, low-frequency rocking motions referred to as peptide librations. This has given rise to a proposed librational entropy mechanism of elasticity. Peptide librations, suggested by the proposed structure, have recently been observed by means of dielectric relaxation studies over the temperature range of 7 – 70°C, and an experimental dipole moment for the dielectric relaxation has been estimated. In this report is presented a calculation of the dipole moment change to be expected from the peptide librations of a pentamer in the β-spiral conformation of the elastin polypentapeptide and of the D·Ala5-polypentapeptide analog. While the experimentally derived and the theoretically calculated values are approximate, the comparison of experimental and calculated values is satisfactory and permits continued serious consideration of the dynamic β-spiral conformation proposed for the elastomeric polypentapeptide of elastin.