Linear free-energy model description of the conformational stability of uracil-DNA glycosylase inhibitor A thermodynamic characterization of interaction with denaturant and cold denaturation

Eur J Biochem. 1999 May;261(3):610-7. doi: 10.1046/j.1432-1327.1999.00271.x.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cold Temperature
  • DNA Glycosylases*
  • Enzyme Inhibitors / chemistry*
  • Escherichia coli / enzymology
  • Guanidine / chemistry
  • Models, Chemical
  • N-Glycosyl Hydrolases / antagonists & inhibitors*
  • Protein Conformation
  • Protein Denaturation
  • Thermodynamics
  • Uracil-DNA Glycosidase

Substances

  • Enzyme Inhibitors
  • DNA Glycosylases
  • N-Glycosyl Hydrolases
  • Uracil-DNA Glycosidase
  • Guanidine