ABSTRACT
This section considers the physical stability of the peptide or protein including conformational changes, aggregation, and adsorption. The physical stability of the protein, and thus protein function, can be affected by a number of environmental parameters. Relatively small changes in temperature, pressure, pH, or concentration of denaturing agents (e.g., guanidine hydrochloride, surfactants), or exposure of the macromolecule to mechanical disruption can lead to an irreversible loss of protein function. The primary mechanism for protein inactivation by these agents or processes involves the denaturation or unfolding of the protein macromolecule. Protein unfolding refers to the loss of tertiary structure and the formation of a disordered protein in which the proper intramolecular contacts within the protein no longer exist. The intermolecular recognition events necessary for proper protein folding are usually cooperative and reversible upon removal of the denaturing agent. However, unfolding can be followed by secondary irreversible inactivating processes such as the chemical changes described in Chapter 2, or by other physical processes such as aggregation of the protein to form higher-order oligomers or “aggregates” and adsorption to surfaces. Therefore, the preservation of protein tertiary structure becomes paramount for preventing losses in protein function. Although scientists have made signifi cant progress in understanding and predicting protein folding, the numerous molecular determinants that drive intraprotein recognition events make protein stabilization an interesting challenge for the protein formulator.
