The collagen-like triple helix to random-chain transition: Experiment and theory

Abstract

The thermal stabilities in solution of guinea pig skin collagen and three synthetic polytripeptide models for collagen, poly( l-prolyl- l-seryl-glycyl), poly( l-prolyl- l-alanyl-glycyl), and poly( l-prolyl-glycyl- l-prolyl), were monitored by observing the temperature-dependence of the circular dichroism spectra. Analysis of the melting temperatures for these polytripeptide sequences suggested a number of factors which should be included in a description of the thermodynamic stability of the collagen triple helix. Among these contributions are: (a) the primary sequence; (b) the molecular weight and polydispersity of the polymer; and (c) the extent of polymer-solvent interaction. A semi-empirical equation incorporating these factors was derived to describe the two-state triple helix to random-chain transition. The enthalpy and entropy parameters employed in the equation, with the exception of those involving polymer-solvent interactions, were calculated by theoretical conformational analysis. In order to evaluate the polymer-solvent interaction energies, it was necessary to calibrate the equation for each solvent system. The predicted versus observed melting temperatures were compared for the synthetic polymers in two solvents of different polarities, water and 1,3-propanediol.