You are studying a protein that you call Protein X. There is an aspartic acid at a key position in Protein X that is important in the folding and stabilization of that protein. If this aspartic acid is changed to a different amino acid, which one of the following amino acid substitutions is MOST likely to allow the protein to fold normally?

threonine

arginine

serine

glycine

glutamic acid

glutamic acid

Explanation:

Aspartic acid or aspartate is a polar amino acid and is negatively charged. It is generally present on the surface of the proteins so that it can interact with the aqueous environment. Sometimes it can be buried within the protein and play a role in stabilization of the protein. It pairs with a positively charged amino acid to form hydrogen bonds which increases the stability of the protein.

If aspartic acid has to be substituted with other amino acid without affecting the protein structure and stability it has to be with a negatively charged polar amino acid like it. Glutamic acid is very similar to aspartic acid in structure and has same polarity. It just has a smaller side chain compared to aspartic acid. So substitution with glutamic acid will most likely allow the protein to fold normally.