title: Linear free-energy model description of the conformational stability of uracil-DNA glycosylase inhibitor A thermodynamic characterization of interaction with denaturant and cold denaturation.
abstract: The equilibrium unfolding of uracil DNA glycosylase inhibitor (Ugi), a small acidic protein of molecular mass 9474 Da, has been studied by a combination of thermal-induced and guanidine hydrochloride (GdnCl)-induced denaturation. The analysis of the denaturation data provides a measure of the changes in conformational free energy, enthalpy, entropy and heat capacity DeltaCp that accompany the equilibrium unfolding of Ugi over a wide range of temperature and GdnCl concentration. The unfolding of Ugi is a simple two-state, reversible process. The protein undergoes both low-temperature and high-temperature unfolding even in the absence of GdnCl but more so in the presence of denaturant. The data are consistent with the linear free-energy model and with a temperature independent DeltaCp over the large temperature range of unfolding. The small DeltaCp (6.52 kJ.mol-1.K-1) for the unfolding of Ugi, is perhaps a reflection of a relatively small, buried hydrophobic core in the folded form of this small monomeric protein. Despite a relatively low value of DeltaG(H2O), 7.40 kJ.mol-1 at pH 8.3, Ugi displays considerable stability with the temperature of maximum stability being 301.6 K.
authors.affiliation: Molecular Biophysics Unit, Indian Insitute of Science, Bangalor, India.
authors.forename: G B
authors.initials: GB
authors.lastname: Reddy
authors.forename: K
authors.initials: K
authors.lastname: Purnapatre
authors.forename: R
authors.initials: R
authors.lastname: Lawrence
authors.forename: S
authors.initials: S
authors.lastname: Roy
authors.forename: U
authors.initials: U
authors.lastname: Varshney
authors.forename: A
authors.initials: A
authors.lastname: Surolia
mesh_terms: D003080:Cold Temperature; D045647:DNA Glycosylases; D004791:Enzyme Inhibitors / Q000737:chemistry*; D004926:Escherichia coli / Q000201:enzymology; D019791:Guanidine / Q000737:chemistry; D008956:Models, Chemical; D009699:N-Glycosyl Hydrolases / Q000037:antagonists & inhibitors*; D011487:Protein Conformation; D011489:Protein Denaturation; D013816:Thermodynamics; D051981:Uracil-DNA Glycosidase
chemical_list: D004791:Enzyme Inhibitors; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D051981:Uracil-DNA Glycosidase; D019791:Guanidine