Uncovering dehydration in cytochrome c refolding from urea- and guanidine hydrochloride-denatured unfolded state by high pressure spectroscopy.

ABSTRACT: To investigate the dehydration associated with protein folding, the partial molar volume changes for protein unfolding (?V u) in cytochrome c (Cyt c) were determined using high pressure absorption spectroscopy. ?V u values for the unfolding to urea- and guanidine hydrochloride (GdnHCl)-denatured Cyt c were estimated to be 56±5 and 29±1 mL mol-1, respectively. Considering that the volume change for hydration of hydrophobic groups is positive and that Cyt c has a covalently bonded heme, a positive ?V u reflects the primary contribution of the hydration of heme. Because of the marked tendency of guanidium ions to interact with hydrophobic groups, a smaller number of water molecules were hydrated with hydrophobic groups in GdnHCl-denatured Cyt c than in urea-denatured Cyt c, resulting in the smaller positive ?V u. On the other hand, urea is a relatively weak denaturant and urea-denatured Cyt c is not completely hydrated, which retains the partially folded structures. To unfold such partial structures, we introduced a mutation near the heme binding site, His26, to Gln, resulting in a negatively shifted ?V u (4±2 mL mol-1) in urea-denatured Cyt c. The formation of the more solvated and less structured state in the urea-denatured mutant enhanced hydration to the hydrophilic groups in the unfolding process. Therefore, we confirmed the hydration of amino acid residues in the protein unfolding of Cyt c by estimating ?V u, which allows us to discuss the hydrated structures in the denatured states of proteins.

SUBMITTER: Konno S 

PROVIDER: S-EPMC6373425 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature