2. A researcher has developed a program to evaluate the stability of a protein by substituting each amino acid at a time by the other 19 amino acids. For a protein, a researcher has observed the following changes in stability upon substitution of amino acids in loops, helices, sheets, protein core and on the protein surface.

   

   a) loops are more tolerant   b) sheets are more tolerant   c) core is less tolerant,   d) helices are less tolerant     e) surface is more tolerant

   Which of the above statements are correct?

   (1) a and c (2) c and d          (3) b and e    (4) a and b

How Amino Acid Substitutions Affect Protein Stability

Proteins are dynamic molecules whose stability depends on their structural components. A researcher developed a program to analyze stability changes by substituting each amino acid with 19 others. The study revealed key insights into the tolerance levels of different protein regions.

Tolerance Levels for Protein Structures

Amino acid substitutions affect different components of the protein in distinct ways:

1. Loops Are More Forgiving

Loops are flexible regions that can accommodate a large variety of amino acid changes with minimal effect on overall stability.

2. Sheets Are More Forgiving

Beta-sheets resist substitution well, showing high tolerance to amino acid replacements.

3. The Protein Core Is Less Tolerant

The protein core is hydrophobic and compact, making it highly sensitive to substitutions that could disrupt stability.

4. Helices Are Less Tolerant

Alpha-helices rely on specific amino acid interactions for stability, making them less adaptable to substitutions.

5. Surface Is More Tolerant

The protein surface is exposed to the external environment and can accommodate substitutions with minimal impact on structure and function.

Correct Answer: b and e

The study confirms that beta-sheets and protein surfaces are more tolerant of amino acid substitutions. This is highly significant for protein design, drug development, and understanding protein evolution.