Statistical thermodynamic treatment of conformational transitions of monomeric and oligomeric proteins

Abstract

The conformational transitions of monomeric and oligomeric proteins as manifested in the heat capacity changes associated with thermal unfolding were quantitatively analysed on the assumption that proteins can be treated as members of a canonical ensemble. This treatment permits the calculation of the partition function Y(T, p) relative to the native state. The second derivative of Y(T, p) with respect to temperature represents perfectly the experimental heat capacity curve of the protein. The proper analysis of the statistical thermodynamic model results in an intriguing phenomenon for all transitions except for the simplest case ND: the proportionality between the enthalpy and the population shift is lost. It is shown that this phenomenon can be both rationalised theoretically and verified experimentally for the N₂2D transition of the protein ROP.