6) (40 points) Ligand binding. Ligand binding to proteins A and B is characteriz

Question

6) (40 points) Ligand binding. Ligand binding to proteins A and B is characterized by the plots shown below H 2.3 1H-1 nH-1 “1 " 0.5 log IL] og [L] (20 points) What are these types of plots called? Which proteins show cooperative ligand binding? What conclusions about the type of cooperativity of the binding can you draw from these plots? Explain the different shape of the binding curves with respect to ligand concentration. what is the minimal number of ligand binding sites on protein molecule for B. (20 points) Based on these plots, each of the proteins. Clearly explain.

Explanation / Answer

Ans:

Ligand Binding to Proteins

Q.1

Ans: The studies of ligand binding are performed by adding ligand to a certain amount of protein X. The fraction () of protein bound to ligand was assessed by measuring the concentration of the protein A and B bound to ligand. These plots are called as Hill Plots.

Both the proteins A and B will show the cooperative ligand binding.

Protein A shows the positive co-operativity as nH > 1, and

The protein B has negative co-operativity as nH < 1.

This positive and Negative co-operativity will determine the shape of the binding curves

A has a transition from low-affinity to a high-affinity binding

B has a transition from high-affinity to low-affinity binding.

Q. 2

Ans: The number of binding sites nH.

For protein A, nH = 2.3, so the minimal integer number nH is 3.

Similarly, for protein B, nH = 0.5, so the minimal number is of ligand binding sites is 2. The minimal integer nH is 1, but at least two binding sites are required for cooperativity.

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