Investigation of the Mechanism of Protein Denaturation by Guanidine Hydrochloride-Induced Dissociation of Inhibitor-Protease Complexes

Abstract

In this communication we describe an approach in which guanidine hydrochloride-induced dissociation of a protein inhibitor-serine protease complex is used to explore the molecular basis of protein denaturation. The rationale behind this approach is that the inhibitor-protease complex is stabilized by the same types of non-covalent interactions that stabilize the native state of a protein. The dissociation of inhibitor-protease complex can be performed at concentrations of guanidine hydrochloride at which the inhibitor and the protease retain their native conformations. Here, we present our results on the effect of 0.1M to 0.4M guanidine hydrochloride concentrations on the association equilibrium constants (reciprocal of dissociation constant) of P1G, P1A, P1V, P1N, and P1S variants of turkey ovomucoid third domain with bovine α-chymotrypsin. We use these results to calculate the free energy change in the dissociation of inhibitor-protease complexes (the m value) per mol of guanidine hydrochloride concentration. Our results agree with the general consensus that the denaturing effect of guanidine hydrochloride is due to its favorable interaction with the polar parts of proteins and that the non-polar side chains have no or little favorable interaction with guanidine hydrochloride. Keywords: Chymotrypsin, denaturation, osmolytes, protease inhibitor, serine proteases, turkey ovomucoid third domain