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The magnitude of changes in guanidine‐HC1 unfolding m‐values in the protein, iso‐1‐cytochrome c, depends upon the substructure containing the mutation
Author(s) -
Hammack Barbara,
Attneld Kathleen,
Clayton Daniel,
Dec Eric,
Sarisky Catherine,
Bowler Bruce E.,
Dong Aichun
Publication year - 1998
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1002/pro.5560070814
Subject(s) - guanidine , chemistry , protein folding , equilibrium unfolding , crystallography , denaturation (fissile materials) , cytochrome c , native state , stereochemistry , biophysics , circular dichroism , biochemistry , biology , mitochondrion , nuclear chemistry
Hydrophilic to hydrophobic mutations have been made at 11 solvent exposed sites on the surface of iso‐1‐cytochrome c . Most of these mutations involve the replacement of lysine with methionine, which is nearly isosteric with lysine. Minimal perturbation to the native structure is expected, and this expectation is confirmed by infrared amide I spectroscopy. Guanidine hydrochloride denaturation studies demonstrate that these variants affect the magnitude of the m ‐value, the rate of change of free energy with respect to denaturant concentration, to different degrees. Changes in m ‐values are indicative of changes in the equilibrium folding mechanism of a protein. Decreases in m ‐values are normally thought to result either from an increased population of intermediates during unfolding or from a more compact denatured state. When cytochrome c is considered in terms of its thermodynamic substructures, the changes in the m‐value for a given variant appear to depend upon the subtructure in which the mutation is made. These data indicate that the relative stabilities and physical properties of substructures of cytochrome c play an important determining role in the equilibrium folding mechanism of this protein.