Globular Protein Stability

A knowledge of the origin of the stability of proteins in aqueous solution is essential to the understanding of their structure and function. The stability of a globular protein in aqueous solution can be determined by studying the disruption of its native structure, i.e., the process of denaturation[1]. In this process the native folded protein structure is converted into a form that is predominantly unfolded but can still possess some residual folded structure[2]. Consequently, the fully unfolded or random-coil state of protein, which is the ideal reference state in discussions of the thermodynamic stability of proteins, is not always experimentally accessible[2]. Through model systems consisting of peptides or shortened proteins, it is

This may be attributed to the fact that the addition of sugars to the protein increases the hydrophobic, electrostatic and hydrogen-bonding interactions giving rise to the compact form of protein. Therefore, by observing a decrease in the compressibility of the solution and the increase in the apparent molal volume of the protein after the addition of sugars, we can say that the extent of denaturation of protein is reduced and its stabilization has taken place Proteins are stabilized by a combination of hydrogen-bonding interactions, electrostatic interactions and hydrophobic interaction. In some proteins there is an additional contribution from cross-linking, metal complexing and specific binding of ions and cofactors. In discussing the effect of different sugars on the stability of hemoglobin, we have to consider the effects of different sugars on these various forces and interactions. In aqueous solutions of protein, there is a cooperative hydrogen–bonded structure.[6] When sugar is added to the protein solution, the OH groups of sugars may also compete for hydrogen-bonding.[6] Now we have to consider the respective interactions between protein, water and additive (sugar) molecules. The additive interacting more strongly with protein than with water will tend to stabilize the denatured states by the formation of protein additive complexes. They will, therefore, have a denaturing effect. However, additives interacting more stronglywith water molecules than with protein will favour the stabilization of protein