Unfolding, reversible thermal, protein

Pohl (1968a,b, 1969, 1972a,b) developed a simple method (which was in fact a slow temperature jump method) to follow reversible thermal unfolding of globular proteins. Reversible denaturation of trypsin, chymotrypsin, and chemically modified derivatives (i.e., anthranyloyl chymotrypsin and diisopropyl chymotrypsin) and ribonuclease A were studied. The thermal denaturation was followed for different pH values. From the data obtained for chymotrypsin as well as for trypsin, Pohl (1968a,b) concluded that there was a two-state process. This conclusion was supported by the following arguments ... 

The van t Hoff plots for thermal denaturation of proteins are linear in the transition region, thus allowing the enthalpy change (AHm) of unfolding at the transition temperature (Tm) to be estimated. Because of the change in free energy in (AG) = 0 at Tm (reversible process), the entropy of unfolding (ASm) at the transition midpoint can be calculated from ... 

Koepf, E.K., Petrassi, H.M., Sudol, M., and Kelly, J.W. 1999. WW An isolated three-stranded antiparallel P-sheet domain that unfolds and refolds reversibly evidence for a structured hydrophobic cluster in urea and GdnHCl and a disordered thermal unfolded state. Protein Sci. 8 841-853. 

Commonly, the thermal denaturation of proteins is often discussed in terms of the Lumry-Eyring model, which involves two steps reversible unfolding and irreversible alteration of the unfolded state to produce the final denatured state, which is unable to fold back to the native protein. 

Unfolding can also be induced by temperature, and thermal denaturation curves (melting curves) are experimentally easier to obtain, since measurements are carried out only on a single protein solution. It is also easy to check the reversibility of the process by slowly cooling the denatured protein solution. The parameter A G°s can be obtained from melting curves provided either that the van t Hoff plot... 

In general, the heating rate dependence of protein thermal structural perturbations can be understood in terms of the Lumry-Eyring model [38], as shown below. According to this framework, a reversible unfolding step is followed by an irreversible event ... 

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