Theoretical study of the thermoelastic properties of elastin model chains

The origin of the elastic behaviour of the bioelastomer elastin has been a matter of some controversy in recent years, as has been the degree of stable secondary structure present in the native state. Available data on the primary sequence of the protein chains constituting the elastin network has indicated a significant incidence of three repeat peptides of length four, five and six, with all containing a Pro-Gly pair within them. The present investigation involved the calculation of the temperature coefficient of the mean-square end-to-end distance 〈r2〉0 of random-coil model chains composed exclusively of one of the three repeat peptides. This configuration-dependent property is directly related to the experimentally obtained energetic component of the elastic force. The values of dln 〈r 2 〉 0 d T for each model chain were evaluated through the use of semi-empirical energy calculations on terminally-blocked residues present in the aforementioned repeat peptides, and subsequent use of established matrix techniques for calculating 〈r2〉0 for polypeptides within a scheme involving independently rotating virtual bonds. Three levels of hydrogen bonding inclusion were investigated to help establish the importance of this contribution. The small positive value of the energetic component of the elastic force for elastin in the literature was found to be adequately reproduced in these calculations on the random-coil model chains.