Heat and cold denatured states of monomeric λ represser are thermodynamically and conformationally equivalen

Although the denaturation of proteins by low temperatures is a well-documented phenomenon, little is known about the molecular details of the process. In this study, the parameters describing the denaturation thermodynamics of residues 6-85 of the N-terminal domain of λ repressor have been determined by fitting the three-dimensional thermal-urea denaturation surface obtained by circular dichroism. The shape of the surface shows cold denaturation at low temperatures and urea concentrations above 2 M, which allows accurate determination of the apparent heat capacity of denaturation (ΔCp). Denaturation curves based on aromatic 1H NMR spectra give identical denaturation curves, confirming purely two-state folding under all conditions studied. The denaturation surface can be fit with constant ΔCP and δ In KD/δ[urea] (KD is the equilibrium constant for denaturation), consistent with a thermodynamically invariant denatured state. In addition, the aromatic 1H NMR spectrum of the cold denatured state at 0 °C in 3 M urea is essentially identical to the spectrum at 70 °C in 3 M urea. These observations indicate that the structures of the cold and heat denatured states, in the presence of 3 M urea, are thermodynamically and conformationally equivalent.

Duke Scholars

Author Terrence Gilbert Oas Biochemistry