Conformational selection or induced fit? New insights from old principles

TL;DR

This paper reevaluates the roles of conformational selection and induced fit in biomolecular interactions, using kinetic models to clarify their contributions and conditions under which each mechanism dominates.

Contribution

It provides a detailed analysis of conformational selection and induced fit mechanisms, including conditions for their dominance and their implications for enzyme kinetics.

Findings

Conformational selection alone predicts Michaelian kinetics.

Induced fit is necessary for the nonlinear behavior of glucokinase.

When both mechanisms coexist, induced fit dominates the net flux.

Abstract

A long standing debate in biochemistry is to determine whether the conformational changes observed during biomolecular interactions proceed through conformational selection (of preexisting isoforms) or induced fit (ligand-induced 3D reshaping). The latter mechanism had been invoked in certain circumstances, for example to explain the non-Michaelian activity of monomeric enzymes like glucokinase. But the relative importance of induced fit has been recently depreciated in favor of conformational selection, assumed to be always sufficient, predominant in general and in particular for glucokinase. The relative contributions of conformational selection and induced fit are reconsidered here in and out of equilibrium, in the light of earlier concepts such as the cyclic equilibrium rule and the turning wheel of Wyman, using single molecule state probability, one way fluxes and net fluxes. The conditions for a switch from conformational selection to induced fit at a given ligand concentration are explicitly determined. Out of equilibrium, the inspection of the enzyme states circuit shows that conformational selection alone would give a Michaelian reaction rate but not the established nonlinear behaviour of glucokinase. Moreover, when induced fit and conformational selection coexist and allow kinetic cooperativity, the net flux emerging in the linkage cycle necessarily corresponds to the induced fit path.