4.16 : Protein Denaturation

The function of proteins depends on their native three-dimensional structure, which is dictated by the amino acid sequence of the specific protein. Folding of the polypeptide chain takes place under specific conditions that energetically favor the folded conformation. In contrast, protein denaturation occurs spontaneously under unfavorable conditions that disrupt the integrity of the folded conformation. Thus, the chemical and physical environment of a protein, such as significant changes in pH or temperature, influences its stability. In addition, the presence of certain organic compounds, salts, and heavy metals can also lead to protein denaturation.

Temperature-induced Protein Denaturation

When proteins are exposed to a higher temperature, the primary non-covalent interactions, including hydrogen bonds, electrostatic forces, and van der Waals interactions, are disrupted. This is because of the rise in the kinetic energy of molecules due to heat that results in their vigorous vibration. Because of the disorder in non-covalent interactions, the native conformation of protein collapses, leading to denaturation. For example, albumin— a protein found in eggs, coagulates when an egg is boiled.

Organic Compounds Induced Protein Denaturation

Various organic compounds have the potential to denature proteins. One such chemical is ethyl alcohol, used in sanitizers and disinfectants owing to its denaturing properties. The alcohol disrupts the side chain intramolecular hydrogen bonds within the protein and forms new hydrogen bonds with the protein side chains. This affects the protein's tertiary structure, resulting in the unfolding of the polypeptide chain and denaturation of the protein.

Heavy Metals Induced Protein Denaturation

Heavy metals such as arsenic, mercury, cadmium, chromium, and lead are toxic because they affect the physiological activities of proteins in the body. These heavy metals either displace the essential metal ion in metalloproteins or form a complex with a functional side chain of the protein. This induces conformational changes in the native structure, hampering the protein's biological activity. For example, metal ions such as calcium in metalloproteins and zinc in zinc-finger proteins are replaced when a person is exposed to cadmium