Could you get cooperativity without allosteric communication between the subunits of the binding protein?
Yes – you could have a multivalent ligand binding to a multi-subunit protein. The classic example is an antigen with repeated structural features, or epitopes (for example, the surface of a bacterium or a virus) interacting with the two arms of an antibody. The binding of one antigen epitope to the antibody makes the second binding event much more favorable by forcing the antigen’s second epitope into close proximity of the antibody’s remaining free antigen binding site. This type of cooperative interaction is often referred to as enforced proximity, or the avidity effect, and it is common in protein-protein interactions. While the avidity effect is similar to KNF cooperativity in that one binding event promotes the next, it is different in terms of the consequences for the shape of the saturation curve. Because the first binding event promotes a zero-order second binding event (that is, it occurs within the complex rather than between the complex and a second ligand), the result here
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- Could you get cooperativity without allosteric communication between the subunits of the binding protein?
