If you are performing site-directed mutagenesis to test predictions about which residues are essential for a protein's function. Which of each pair of amino acid substitutions listed below would you expect to disrupt protein structure the most? And why? how do you go abouts knowing this?

O Pro replaced by Gly or His,

O Gln replaced by Glu or Asn,

O Lys replaced by Asp or Arg

O Gln replaced by Glu or Asn

Explanation:

Gln replaced by Glu or Asn, is a non-conservative substitution. Gln has a much shorter side chain or R-group than Glu or Asn. Additionally both Glu and Asn R-groups are polar and negatively charged while Gln is non-polar. In a protein, replacement with Glu or Asn would greatly destabilize the protein by introducing a charge and disrupting hydrophobic interactions formed between Gln and other non-polar residues. By comparing the R-groups of the residues, their length, hydrophobicity, charge and shape. One can predict if the substitution is disruptive or not, if residues are very similar then the interactions that they form are preserved. For example replacing Gln with Ala would be less disruptive.