Question

2) Disulfide bonds determine the properties of many proteins. A number of natural proteins are very rich in disulfide bonds and their mechanical properties (tensile strength, viscosity, hardness, etc.) are correlated with the degree of disulfide bonding. For example, glutenin, a wheat protein rich in disulfide bonds is responsible for the cohesive and elastic character of dough made form wheat four. The hard, tough nature of tortoise shell is due to the extensive disulfide bonding in its a-keratin.

What is the molecular basis for the correlation between disulfide bond content and mechanical properties of the protein? Then compare disulfide bonds with the other class of bonds discussed in class (and in the book) and how these other bonds influence protein folding. Two examples of other bond types are sufficient.

Answer 1

Proteins have my interatomic interactions in the form of hydrophobic bonds, electrostatic interactions (salt bridges) and Van der Waal's forces but these are quite weak and mostly contribute to the stability of the protein in its native state.

On the contrary Disulfide bonds are strong covalent bonds, then supersede the other forces of attraction in proteins (as demonstrated by Anfinsen's experiment) and constraint protein folding. If the disulfide bonds are formed before hydrogen bonds/electrostatic bonds then the protein folds in a manner such that disulfide bonds are not disturbed, the other bonds have to adjust according to the disulfide bonds.

Being the strongest bond in proteins, disulfide bonds are said to contribute to the mechanical properties of a protein.