Entropic Elastic Processes in Protein Mechanisms. Part 1. Elastic Structure Due to an Inverse Temperature Transition and Elasticity Due to Internal Chain Dynamics

摘要

Numerous physical characterizations clearly demonstrate that a polypentapeptide of elastin, in water undergoes an inverse temperature transition. At fixed extension of the cross-linked polypentapeptide elastomer, development of elastomeric force is seen to correlate with increase in intramolecular order, that is, with the inverse temperature transition. Reversible thermal denaturation of the ordered polypentapeptide is observed with composition and circular dichroism studies, and thermal denaturation of the cross-linked elastomer is also observed with loss of elastomeric force and elastic modulus. The implications of these findings to elastic processes in protein mechanisms are several: i. When elastic processes are observed in proteins, it is not necessary, and it may be incorrect, to attempt description in terms of random chain networks and random coils. ii. Rather than requiring a random chain network characterized by a random distribution of end-to-end chain lengths, entropic elastomeric force can be exhibited by a single, short peptide segment. iii. Perhaps of greatest significance whether occurring in a short peptide segment or in a fibrillar protein, it should be possible reversibly to turn on and off elastomeric force by reversibly changing the hydrophobicity of the polypeptide. Phosphorylation and dephosphorylation would be the most obvious means of changing the hydrophobicity of a polypeptide. These considerations are treated in the second paper, PART 2: Simple (Passive) and Coupled (Active) Development of Elastic Forces.