You are studying the binding of serine to its receptor protein. The side chain of Ser makes two H-bonds to the receptor, one to the side chain of a Thr and one to a backbone carbonyl of a Lys. You wish to study the importance of these interactions by mutagenesis and binding experiments.

a.You generate the Thr?Ala mutant, but not the Lys?Ala mutant.Why?

b.The Thr?Ala mutant binds 2-fold less tightly than the normalprotein. Draw a graph below that shows both binding curves.

c.The 2-fold loss in binding corresponding to a change in ?G of0.7 kcal/mol is less than 5 – 6 kcal/mol you might have expected an H-bond to be worth. Suggest an explanation.