Question

Protein 5 (TRP5), which is 145 amino acids in length and is expressed in human neurons. TRP5 binds a small organic molecule (GTBH) in a cavity on its surface. (This binding is non-covalent, non-enzymatic, and reversible.)

You are designing a drug (NSRNH), to inhibit the binding of GTBH to TRP5. You want the binding of NSRNH to TRP5 to be a strong association. Which of the following should be exhibited by a NSRNH-TRP5 complex?

a high Ka

a low Ka

a low Kd

a high Ka and a low Kd

None of these answer choices is correct.

Answer 1

Ka is called association constant and Kd is called dissociation constant. Binding affinity is usually measured with equillibrium dissociation constant. Lower the Kd, greater would be the binding affinity of the ligand to the target and since Ka is reciprocal of Kd it also means higher the Ka, greater would be binding affinity of the ligand to the target.

So answer is a high Ka and a low Kd should be exhibited by a NSRNH-TRP5 completx so that the binding of NSRNH to TRP5 would be a strong association.