Question

Biochemistry 4. What are the two models for the interconversion of inactive and active during protein cooperative ligand binding ?

Answer 1

Two models are-

1) sequential model (also known as KNF model)

This describes cooperativity of protein subunits. According to this model protein conformation changes with each binding of ligand. This model follows structural theory of induced fit model of substrates binding to enzyme, any or slight change in confirmation of enzyme improves it's binding affinity to transition state of ligand. Two main assumptions of this models are -

•The protein exists in single state of either low or high affinity for ligand,when not bound to the ligand

• When ligand binds on site, a confirmational changes is produced in that region of protein and this may influence the conformation of nearby binding sites on same protein. Hence changing their affinity for ligand.

2) Monod-Wyman-Changeux model (also known as symmetry model)

According to this model the concept of two distinct symmetric states is the main postulate. The regulated protein, such as many enzymes and receptors, exist in different interconvertible states in absence of any regulator. The conformational states is determined by thermal equilibrium.