Fluxes for Unraveling Complex Binding Mechanisms

A decade ago, many high-affinity drugs were thought to bind to their target via an induced-fit pathway instead of conformational selection. Yet, both pathways make up part of a thermodynamic cycle, and, owing to binding flux-based approaches, it is now rather considered that they act in parallel and also that their relative contribution to the final ligand-target complex depends on the ligand concentration. Those approaches are of increasing interest, but published data still merely refer to the peculiar situation of equilibrium binding. This article draws attention to the benefit of extending those approaches to address more physiological nonequilibrium binding conditions and in vivo situations. For the presented example, they help to apprehend transient experimental manifestations of a 'conventional' thermodynamic cycle.