2 Protein structure interactions 120 pts Human growth hormo

2) Protein structure & interactions 120 pts]. Human growth hormone (hGH) binds to the hGH binding protein (hGHbp) with a Kd of 1 nM. Mutations in hGHbp at the protein-protein interface lead to significant decreases in binding affinity. Some of the largest effects come from single mutations of 103 or W104 to alanine. a) [5 pts] What is your prediction for the Kd for binding between hGH and the double mutant I103A/W104A hGHbp? Use the K d values given for the I103A and W104A single mutants below, and assume I 103 and W104 mutations are completely independent in their effects on hGHbp structure and interactions with hGH hGHbp (wt) hGHbp (W104A) Kd 0.34 nM Kd 1.0 uM hGHbp (103A) hGHbp (1103Aww104A) 5.1 nM Kd b) [5 pts] When you measure the Kd for I 103A/W104A hGHbp binding to hGH, you obtain a value of 1.0 uM. Provide a brief, general explanation (1-2 sentences) for why this result differs from your prediction c) [10 pts]. Using the structure from the pdb file la22, provide a structural explanation for why the observed Kd differs from your prediction. Keep your explanation brief (1-3 sentences). It may help to consider the hGH residues in close proximity (i.e s 4A) to both I103 and W104 *Note: for reasons unknown, the pdbfile la22 starts numbering residues in hGHbpfrom 201, so W104 is listed as W304 in the padb file.

Solution

1. Kd of the double mutants will not be more than the Kd of single mutants. Because the mutations in alanine double mutants is non additive mutants. Hence it is not more than the Kd of single mutants.

2. Mutation in alanine at w104 makes complete loss of site 1 HGH binding. Hence the Kd remains 1.0micro molar .

3.