An oligomeric protein binds its ligand cooperatively according to the two-state
ID: 213124 • Letter: A
Question
An oligomeric protein binds its ligand cooperatively according to the two-state allosteric model diagrammed below. In this model, the ligand binds preferentially to the protein’s R state.
In the absence of ligand, the wild-type protein exists primarily in the T state. A mutant version of the protein, however, exists primarily in the R state, even in the absence of ligand.
Which would exhibit higher affinity, wild-type or mutant protein? Why?
Which would exhibit a higher degree of cooperativity, wild-type or mutant protein? Why?
T state R state binds ligand poorly binds ligand tightly 88-EExplanation / Answer
Ans:
The rate of binding is generally known as affinity, it is a measurement of the strength of the binding. High-affinity usually results from a higher inter-molecular force, Here the ligand binds strongly to the molecules R state. The mutant version of the molecule exists primarily in the R state, so the ligand will bind with a higher affinity with the mutant protein rather than the wild-type protein.
The wildtype protein will show higher cooperativity. The mutant has a fixed molecular structure, but in the wildtype, as the ligand binds the affinity will gradually increase, showing positive cooperativity.