5. Disulfide Bonds Determine the Properties of Many Proteins Some natural protei
ID: 188353 • Letter: 5
Question
5. Disulfide Bonds Determine the Properties of Many Proteins Some natural proteins are rich in disulfide bonds, and their mechanical properties (tensile strength, viscosity, hardness, etc.) are correlated with the degree of disulfide bonding (a) Glutenin, a wheat protein rich in disulfide bonds, 1s responsible for the cohesive and elastic character of dough made from wheat flour. Similarly, the hard, tough nature of tortoise shell is due to the extensive disulfide bonding in its -keratin. What is the molecular basis for the correlation between disulfide-bond content and mechanical properties of the protein? b) Most globular proteins are denatured and lose their activity when briefly heated to 65 °C. However, globular pro- teins that contain multiple disulfide bonds often must be heated longer at higher temperatures to denature them. One such protein isbovine pancreatic trypsin inhibitor (BPTD which has 58 amino acid residues in a single chain and con- tains three disulfide bonds. On cooling a solution of denatured BPTI, the activity of the protein is restored. What is the molecular basis for this property?Explanation / Answer
Answer a.) Glutenins are polymeric proteins (i.e. formed from subunits linked by disulphide bonds) with molecular weights from 100,000 up to many millions. These high-molecular-weight glutenins are formed by disulfide linkages of several diverse polypeptide chains. The linkage of these proteins in a fairly linear array contributes to the unique viscoelastic properties of glutenin.
Keratin is a fibrous protein which is formed by all vertebrates for making substances like hair, wool, nails, claws and shells. Chemically keratin is formed by polypeptide chains joined by hydrogen bonds, salt cross bridges and disulphide linkages. -keratin is especially responsible for the formation of hard and strong proteins with toughness, elasticity and insoluble nature of the protein. Such proteins are rich in hydrophobic amino acids and their strength is provided by the disulphide bridges that provide cross-linking networks thereby increasing the strength and prevents folding of the proteins.
Answer b.) In the BPTI protein its conformational stability is detemined by the intra-chain cross-linking disulphide bonds. When the protein is heated and denatured, these disulphide bonds prevent complete unfolding of the protein. Thus upon cooling, the activity of this protein is restored.
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