Why are post-translational modifications necessary for many secreted proteins?

Why are post-translational modifications necessary for many secreted proteins?

• A. Secreted proteins often require specific folding, processing, glycosylation, and targeting to function properly and reach their destinations.
• B. Post-translational modifications are not necessary for protein function.
• C. They only modify DNA sequences.
• D. They only occur in cytosolic proteins.

Answer: (D)

Post-translational modifications allow secreted proteins to fold correctly, be processed, and be targeted to their proper destinations outside the cell. These proteins are made with signals that direct them into the secretory pathway, beginning in the endoplasmic reticulum where folding is assisted by chaperones and disulfide bonds form. The signal peptide is often removed as part of maturation. Glycosylation, added in the ER and refined in the Golgi, increases stability, solubility, and proper folding, and also helps with trafficking and cell recognition. Proteolytic processing can further activate the protein by removing propeptides. All these steps ensure the secreted protein achieves the correct structure, activity, and extracellular localization. In contrast, post-translational modifications do not modify DNA sequences, and they are not limited to cytosolic proteins; they occur throughout the secretory pathway to prepare proteins for secretion.

Post-translational modifications allow secreted proteins to fold correctly, be processed, and be targeted to their proper destinations outside the cell. These proteins are made with signals that direct them into the secretory pathway, beginning in the endoplasmic reticulum where folding is assisted by chaperones and disulfide bonds form. The signal peptide is often removed as part of maturation. Glycosylation, added in the ER and refined in the Golgi, increases stability, solubility, and proper folding, and also helps with trafficking and cell recognition. Proteolytic processing can further activate the protein by removing propeptides. All these steps ensure the secreted protein achieves the correct structure, activity, and extracellular localization. In contrast, post-translational modifications do not modify DNA sequences, and they are not limited to cytosolic proteins; they occur throughout the secretory pathway to prepare proteins for secretion.