Figure 2.

Possible mechanisms for coupled folding and binding, illustrated using the proteins pKID and KIX. (a) When unbound, an IDP exists as an equilibrium between multiple distinct structures, which may include the fully folded structure. (b) According to the induced fit folding mechanism, the IDP binds to its partner in the unfolded state before (c) folding while attached to its partner. (d) The conformation selection mechanism suggests that the partner protein selects folded structures from the equilibrium ensemble of the IDP, and binds only to them.