Conformational Stability Denaturation and Renaturation

Abstract

In order to perform its biological function, a protein must possess the correct configuration, i.e., it must be in its native state, with the correct secondary, tertiary, and, where applicable, quaternary structure. Under in vivo conditions, this is achieved on the ribosome during the synthesis of the protein. Any mistakes in the folding mechanism are then symptomatic of a pathological condition. Howver, under in vitro conditions of isolation, concentration, drying, and so on, changes may occur that will result in partial or complete inactivation. The protein is then said to be denatured. With the vast majority of proteins, the stability of the native (N) state, relative to the denatured (D) state, is highly marginal, amounting to no more than 60 kJlmo1, which is equivalent to the strength of only 3–4 hydrogen bonds (1). Yet, the native structure usually contains several hundred such bonds. From a biological point of view, this marginal stability is required so that proteins can be turned over rapidly, thus avoiding the buildup of, say, immunoglobulins or hormones in the serum. On the other hand, the labile nature of the native state presents problems for the processor who must avoid extremes of pH, ionic strength, temperature, shear, and so on during the various stages of the isolation and concentration process.