Question

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4. (3 points) Which set of binding data is likely to represent cooperative ligand binding to an oligomeric protein? Explain! (Note: Yor Theta is the percent saturation of receptor with ligand) a. | [Ligand] (mM) | Y 0.1 0.2 0.4 0.7 0.3 0.5 0.7 0.9 b. 0.3 0.4 0.6 0.3 0.6 0.8

Answer 1

Cooperative ligand binding : It is allosteric binding which requiremultiple binding site i.e more than one binding site on the macromolecule.    They are of two types :

1) Positive Cooperative binding : If the binding of one ligand at one site maximises the affinity of binding at another site, then this known as positive cooperative ligand.

2) Negative Cooperative binding : If the binding of one ligand at one site minimises the affinity of binding at another site, then this known as negative cooperative ligand.

Noncooperative binding : If the binding of one ligand is indepedent of the other site then it is noncooperative binding.

The graph between Y i.e percent saturation of receptor with ligand on Y-axis and ligand concentration on X axis for a cooperative binding to oligomeric protein should be in the form of sigmoidal curve wheras for non cooperative binding will be in hyperbolic in shape

​so when the data is plotted DATA B is representing the cooperative ligand binding to an oligomeric protein    Binding data

Ligand (mM)    Y MONOMERIC BINDING (HYPERBOLIC CURVE)

0.1 0.3

0.2    0.5

0.4    0.7

0.7    0.9 ​LIGAND (mM) Y    SIGMOIDAL SHAPE (OLIGOMERIC COOPERATIVE BINDING)

0.2 0.1

0.3 0.3

0.4 0.6

0.6 0.8