Question

Formation of mature insulin includes all of the following except A. removal of a signal peptide. B. folding into a three-dimensional structure. C. disulfide bond formation. D. removal of a peptide from an internal region. E. \(\gamma\) -carboxylation of glutamate residues.

Short answer

Answer: \(\gamma\)-carboxylation of glutamate residues.

Step-by-step solution

Option A: Removal of a signal peptide

This process is involved in the formation of mature insulin. The signal peptide is a short peptide chain that guides the protein to certain cellular compartments during protein synthesis. It is removed during the maturation process of insulin.

Option B: Folding into a three-dimensional structure

This process is also correct. In order for a protein to be functional, it must fold into its specific three-dimensional structure, called the native conformation. Insulin undergoes this process to acquire its functional structure.

Option C: Disulfide bond formation

Disulfide bond formation is an essential step in the maturation of insulin. It helps stabilize the protein's structure by joining two cysteine residues through a covalent bond, ensuring that the functional three-dimensional structure is maintained.

Option D: Removal of a peptide from an internal region

During the maturation process of insulin, a small peptide called C-peptide is removed from an internal region. This removal is necessary to join the A and B chains of insulin, which ultimately form the mature hormone.

Option E: \(\gamma\)-carboxylation of glutamate residues

This process is not involved in the formation of mature insulin. \(\gamma\)-carboxylation of glutamate residues is a post-translational modification that occurs in certain proteins, such as clotting factors, but not in insulin. Therefore, the correct answer is: Option E: \(\gamma\)-carboxylation of glutamate residues.