Measuring the forces that control protein interactions

Although the force fields and interaction energies that control protein beh avior can be inferred indirectly from equilibrium and kinetic measurements, recent developments have made it possible to quantify directly (a) the ran ges, magnitudes, and time dependence of the interaction energies and forces between biological materials; (b) the mechanical properties of isolated pr oteins; and (c) the strength of single receptor-ligand bonds. This review d escribes recent results obtained by using the atomic force microscope, opti cal tweezers, the surface force apparatus, and micropipette aspiration to q uantify short-range protein-ligand interactions and the long-range, nonspec ific forces that together control protein behavior. The examples presented illustrate the power of force measurements to quantify directly the force f ields and energies that control protein behavior.