inducedfit

Induced fit is a model describing how enzymes and some receptors recognize substrates or ligands by undergoing structural rearrangements after initial contact. In this view, the active site is flexible and only becomes a highly complementary catalyst pocket once the substrate begins to bind, enabling proper alignment of catalytic residues and other functional groups.

The concept was proposed by Daniel Koshland in 1958 as a refinement of the earlier lock-and-key idea, which posited a rigid fit between enzyme and substrate. Evidence accumulated that proteins are dynamic and can adjust their shapes upon binding. Induced fit emphasizes that binding events can actively shape the binding pocket, rather than merely selecting a pre-existing compatible conformation.

Mechanistically, substrate binding typically involves initial weak interactions on the protein surface that destabilize certain regions and trigger movements of loops or side chains. These conformational changes close the pocket around the substrate, realign catalytic residues, and stabilize the transition state, often increasing reaction specificity and rate. The energetic contribution of binding interactions helps drive the structural rearrangements.

Contemporary understanding situates induced fit alongside concepts such as conformational selection, where proteins exist in an ensemble of conformations and binding shifts the equilibrium toward a particular state. In practice, many systems exhibit a combination of both processes. The induced-fit principle also applies to receptor-ligand interactions in signaling, where ligand binding can provoke shape changes that influence affinity and downstream responses.