Folding of Proteins | DNB Based MCQ

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Which of the following is helpful for folding of proteins? 

A. Chaperones 
B. Proteosome 
C. Chaperones 
D. Ligands

Ans. A. (Chaperones)

Explanation
• Protein folding in vivo, the role of molecular chaperones

• The chaperones are major prokaryotic and eukaryotic proteins, with the function of helping in folding of nascent polypeptide chains, helping refolding of denatured proteins, and preventing aggregation of surface-exposed hydrophobic parts of proteins, having problems with folding.

• Chaperones help the proteins to fold, so they increase the speed of folding, by stabilizing unstable intermediates of the appropriate polypeptide chain, and decreasing the activation-energy barriers during folding.

• They do not change the thermodynamics of folding, i.e., the ratio of folded and unfolded polypeptides, they only influence the kinetics of gyration.

• In this sense they are often correlated with the enzymes. However, sometimes they are very similar to them, but sometimes are very different, as they are not too specific for the ligands, they help to fold, the substrates are very large, and their large- scale functions make them key-molecules of the cells.

• Since a protein can fold incorrectly in a lot of ways, so there may be a lot of incorrect intermediates, but the correct folding can occur only in one way in most cases. Mostly they recognize hydrophobic surfaces on the proteins, and prevent them from aggregation.

• Chaperones attach to nascent polypeptide chains and prevent wrong folding so that folding is allowed only in correct directions. They help in tertiary and quatemary structure of protein. They are not part of the protein. They have ATPase activity.