Add time:08/12/2019         Source:sciencedirect.com

In vacuo molecular dynamics simulation using the CHARMm program was carried out on a putative structure (“state III”) of the repeating pentapeptide, (VPGVG), of elastin at two different extensions. “State III” is the proposed structure for the experimental state III which develops after prolonged heating at temperatures greater than 60 °C. “State III” is a helix, called a β-spiral, with 2.9 pentamer units per turn in which the type II β-turns fan outward in propeller fashion and the Val4 side chains turn inward displacing the former intra-spiral water and increasing the intramolecular hydrophobic interactions. The fluctuations in backbone dihedral angles for this “state III” are found to be smaller for the structure on extension. These results are compared with previous calculations on the proposed structure for the physiological state, state II, in which the β-turns function as spacers between turns of the dynamic β-spiral and in which there is much water within the β-spiral. The magnitude of dihedral angle damping upon elongation of “state III” is, however, much smaller than that calculated from the β-spiral structure for state II. The computational result is consistent with the experimental observations of shrinking and expulsion of water and of loss of elastic modulus on heating above 60 °C. The implications of this modelling of state III and state II on the damping of internal chain dynamics on extension are discussed with regard to the source of entropic elasticity.

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