32. A protein has 30% alanine. If all the alanines are replaced by glycines,
    (1) helical content will increase.
    (2) ß-sheet content will increase.
    (3) there will be no change in conformation
    (4) the alanine-substituted protein will be less structured than the parent protein.

Impact of Alanine-to-Glycine Substitution on Protein Structure

Proteins are composed of amino acids that determine their structure and function. Alanine and glycine, despite their small size, play crucial roles in secondary structures like alpha-helices and beta-sheets. Understanding the effect of substituting alanine with glycine helps in predicting structural stability and folding patterns, making this topic vital for CSIR NET Life Science aspirants.

Correct Answer:

The correct option is (4) The alanine-substituted protein will be less structured than the parent protein.

Explanation:

(1) Helical content will increase ❌

Alanine is a strong alpha-helix former, whereas glycine disrupts helices due to its high flexibility. Replacing alanine with glycine would reduce the helical content rather than increase it.

(2) Beta-sheet content will increase ❌

Glycine does not favor beta-sheet formation either. Beta-sheets are usually stabilized by amino acids like valine, isoleucine, and phenylalanine, which have bulkier side chains that support hydrogen bonding networks.

(3) There will be no change in conformation ❌

Replacing 30% of alanine with glycine is a significant modification. The increased flexibility introduced by glycine can disrupt the protein’s structural integrity, leading to potential unfolding or misfolding.

(4) The alanine-substituted protein will be less structured than the parent protein ✅

Glycine is highly flexible and does not strongly support any specific secondary structure. Substituting alanine with glycine reduces structural stability, making the protein more disordered.

Nearby Topics for Better Understanding

1. Role of Alanine and Glycine in Protein Secondary Structure

• Alanine:
  • Strong alpha-helix former.
  • Provides structural stability.
• Glycine:
  • Highly flexible and disrupts helices.
  • Often found in loops and turns due to its conformational freedom.

2. Factors Affecting Protein Stability

• Hydrogen Bonding: Maintains alpha-helices and beta-sheets.
• Amino Acid Composition: Small changes can disrupt stability.
• Steric Hindrance: Bulky side chains stabilize beta-sheets, while small residues like glycine increase flexibility.

3. Alpha-Helix vs. Beta-Sheet Stability

4. Importance of Protein Folding in Biological Functions

• Proper folding ensures enzymatic activity and binding affinity.
• Misfolding can lead to diseases like Alzheimer’s and Parkinson’s.
• Structural modifications impact protein-protein interactions and membrane association.

Conclusion

Replacing alanine with glycine significantly alters protein structure, making it less ordered due to increased flexibility. This highlights the critical role of amino acid composition in protein folding and stability, an essential concept for CSIR NET Life Science aspirants.