Protein Folding and Stability

Abstract

We have seen in Chapter 1 that the biological activity of a protein is directly dependent on the adoption of a specific three-dimensional structure by the polypeptide chain. This correctly folded structure, referred to as the native conformation, is thought to represent not only the most biologically active form of the protein, but also an arrangement of the polypeptide chain of minimal potential energy. While it is true that there is some thermodynamic stability to the native conformation of a protein relative to the unfolded state, this stabilization can be quite modest. It is surprising, but true, that for many proteins the native conformation is stabilized over the denatured form by only a few kcal/mol. Thus it is easy to see why protein stability is often a problem for long term storage or use of proteins in solution. In Chapter 2 we discussed general methods for maximizing the stability of proteins for laboratory purposes. In this chapter we shall explore the use of studying protein unfolding by chemical and thermal means as a measure of the relative stabilities of different proteins or the same protein under different solution conditions.