Suppose that a glutamine residue in the active site of an enzyme was mutated to alanine. As expected, the alanine mutant was inactive, suggesting that the glutamine residue was critical to the catalytic mechanism. Which mutation is most likely to restore wild-type level of activity to the alanine mutant?

A to M

A to N

A to F

A to K

A to E

A to N

Explanation:

Glutamine is an amino acid with a polar, uncharged side chain. The mutation to alanine, an amino acid with a non-polar side chain, completely affects the enzymatic activity. This makes sense considering the difference in the nature of both amino acids.

To restore the wild-type level of activity the alanine would have to mutate to another polar uncharged amino acid. Among the given options, only Asparagine (N) has a similar chemistry to Glutamine.