To assess which residues contribute most to the stability of a protein, mutants of the protein are made in which one residue is replaced by amino acid X. The stability of this mutated protein is then measured and compared to the original protein. By repeating the process for many different positions, residues most important for stability can be determined. What would be a good choice for residue X?

• Pro
• Gly
• Ala
• Lys