Method of determining the relative stability of different conformational states of biopolymer molecules

Abstract

A method for estimating the relative stability of conformational states of biopolymer molecules from the degree of sharpness of the transition between them has been suggested. The method is applied to the estimation of stability of the DNA helical structure under physiological conditions as well as to the estimation of stability of an α-helical structure of polypeptide chains in different solvents. The stability of an α-helical structure of polypeptide chains is relatively low not only in aqueous media but also in water-organic mixtures and even in inert organic solvents in which the energy of intramolecular hydrogen bonds is essentially higher than in aqueous medium. This is an evidence that the formation of the helical structure in organic solvents must be accompanied by a noticeably greater decrease in the conformational free energy of monomer units than in water. This conclusion is confirmed by independent experimental data on free energies of initiation of helical regions of polypeptide chains. For the explanation of this effect an assumption is made on the role of dipole-dipole interactions of peptide groups of the backbone.