Question

Protein A Protein B [PL), UM 0.00 0 0.000 0 1) (10 marks) You study ligand binding to two proteins, A and B. You measured the concentration, (PL), of the ligand-bound form of the protein at various ligand concentrations, [L]. The data are summarized in the two tables below. Note that you do not know the total concentration of the protein, but you know that adding more ligand did not noticeably change the bound- protein concentration. [L), UM [PL], uM [L], UM a. Graph the data with both curves on the same plot (to submit your graphs please paste into either a word or a pdf document along with your solutions) b. Determine the Kd values for each of the proteins. Explain any assumptions you made. Which of the two proteins binds the ligand tighter? Explain your reasoning. 5 0.040 15 0.21 10 0.067 30 0.33 50 0.143 100 0.55 200 0.182 300 0.68 500 0.192 1000 0.74 2000 0.198 3000 0.76 C.

Answer 1

a) The binding curves are for the data given in the question are-

X axis- Ligand concentration

Y axis- concentration of ligand bound form of the protein

Protein A 0.25 0.20- 0.15 20.10- 0.05 0.00 500 1000 1500 2000 2500 -0.05 L

Protein B 0.8- 0.6 0.4- PL 0.2+ 0.0 1000 3000 4000 2000 L -0.2-

b) For protein A-

Best-fit values
Bmax	0.1999
Kd	19.85

For protein B-

Best-fit values
Bmax	0.7701
Kd	40.00

The Kd for protein A- 19.85 uM

Kd for protein B- 40 uM

c) We know that the lower the Kd (the higher the [ML] at any given M and L), the tighter is the binding. The higher the Kd, the looser is the binding.

Thus Protein A binds ligand tighter.