[Equilibrium dynamics of the 3-dimensional structure of globular proteins]

According to the data of many physical and physico-chemical methods for conditions near to physiological, there are two types of spontaneous reversible conformational transitions in native proteins namely, local transconformations and overall unfolding of the molecule. Conformational transitions of both types occur with correlation times of less than 10-1--10-3 sec. Some local transconformations, especially those revealed by the hydrogen exchange method, are characterized by weak temperature dependence of the equilibrium constant (local temperature-independent (TI) transconformations). Combining the data obtained by the hydrogen exchange method with recently published results of energy refinement of protein structure leads us to suggest that the probability of local TI-transconformations is independent of hydrophobic forces and possibly related to the "internal" conformational free energy of the native protein, i.e. the sum of (1) the potentional energy of non-bonded intramolecular interactions, (2) the energy of dihedral and bond angle strain as well as (3) the entropy of the folded protein. In the proposed model of dynamic structure the cooperative nature of local TI-transconformations is a result of close interrelation between the optimization of van der Waals side chain interactions in the nonpolar core and variation of dihedral and valence angles. It is shown that the local TI-conformers are closely related to the functionally important transient key states of native proteins.