Questions: Which of the following amino-acid substitutions is LEAST likely to be disruptive to protein function? Pick the correct answer Arginine to valine Lysine to glycine Aspartate to Glutamate Alanine to proline Cysteine to leucine

The answer is: Aspartate to Glutamate

Explanation for each option:

1. Arginine to valine: This substitution is likely to be disruptive because arginine is a positively charged, polar amino acid, while valine is a nonpolar, hydrophobic amino acid. This change can significantly affect the protein's structure and function, especially if the arginine is involved in ionic interactions or hydrogen bonding.

2. Lysine to glycine: Lysine is a positively charged, polar amino acid, while glycine is a small, nonpolar amino acid. This substitution can be quite disruptive because glycine's small size and lack of side chain can lead to a loss of important interactions and structural stability.

3. Aspartate to Glutamate: Both aspartate and glutamate are negatively charged, polar amino acids. The main difference between them is that glutamate has one extra methylene group (-CH2-). This substitution is least likely to be disruptive because both amino acids have similar properties and can often perform similar roles in the protein structure.

4. Alanine to proline: Alanine is a small, nonpolar amino acid, while proline is a unique amino acid with a rigid ring structure that can introduce kinks in the protein chain. This substitution can be quite disruptive to the protein's secondary structure, particularly if it occurs in an alpha-helix or beta-sheet.

5. Cysteine to leucine: Cysteine is a polar amino acid that can form disulfide bonds, which are important for protein stability. Leucine is a nonpolar, hydrophobic amino acid. This substitution can be disruptive because it removes the potential for disulfide bond formation and changes the local environment from polar to nonpolar.

Summary: The substitution of aspartate to glutamate is least likely to be disruptive to protein function because both amino acids have similar properties, maintaining the overall charge and polarity in the protein structure.