A molecular dynamics investigation of the elastomeric restoring force in elastin

Abstract

A repetitive polypentapeptide organized as a connected chain of β‐bends is believed to be an important structural element of elastin, the major elastomer in biological systems. Molecular dynamics simulations were carried out on hydrated polymers of (Val‐Pro‐Gly‐Val‐Gly)₁₈ at various extensions. Analysis of the fluctuations of backbone angles in relaxed elastin showed that particularly large‐amplitude torsional motions occur in ϕ and ψ angles of residues connecting sequentially adjacent hairpin bends. Many such motions reflect peptide plane librations that result from anticorrelated crankshaft rotations of ψ_i and ϕ_i+1. These effects were much reduced in stretched polymer models. The conformational entropy of relaxed and stretched elastin models was estimated using a treatment due to Meirovitch, and gave a calculated decrease in entropy of about 1 cal/mol deg when the polymer was stretched to 1.75 times its original length. There are large changes in solvent‐accessible surface area during the intitial stages of elastin stretching. Collectively these results suggest that hydrophobic interactions make contributions to elastin entropy at low extensions, but that librational mechanisms make large contributions to the elastic restoring force at longer extensions.