Energy landscapes of receptor–ligand bonds explored with dynamic force spectroscopy

Abstract

Atomic force microscopy (AFM) has been used to measure the strength of bonds between biological receptor molecules and their ligands. But for weak noncovalent bonds, a dynamic spectrum of bond strengths is predicted as the loading rate is altered, with the measured strength being governed by the prominent barriers traversed in the energy landscape along the force-driven bond-dissociation pathway. In other words, the pioneering early AFM measurements represent only a single point in a continuous spectrum of bond strengths, because theory predicts that these will depend on the rate at which the load is applied. Here we report the strength spectra for the bonds between streptavidin (or avidin) and biotins-the prototype of receptor-ligand interactions used in earlier AFM studies, and which have been modelled by molecular dynamics. We have probed bond formation over six orders of magnitude in loading rate, and find that the bond survival time diminished from about 1 min to 0.001 s with increasing loading rate over this range. The bond strength, meanwhile, increased from about 5 pN to 170 pN. Thus, although they are among the strongest noncovalent linkages in biology (affinity of 10(13) to 10(15) M(-1)), these bonds in fact appear strong or weak depending on how fast they are loaded. We are also able to relate the activation barriers derived from our strength spectra to the shape of the energy landscape derived from simulations of the biotin-avidin complex.

A nanomechanical interface to rapid single-molecule interactions

“…Forces as much as 750 pN are measured as well. These values are much higher than the rupture forces previously reported for this molecular complex 7,15,22,23 , which is a consequence of the significantly higher loading rate achieved.…”

“…The loading rate dependency of most likely rupture forces contains information about the energy landscape of receptor-ligand interactions. When measured over a wide dynamic range and plotted on a logarithmic scale, different energy barriers can be resolved from the changes in the slope 15,24,25 . The position of the barrier x β is related to the slope f β by f β = k B T/x β (here k B is Boltzmann constant and T is temperature) 24,26 .…”

“…Consequently, the slow mechanical interface to single-molecule processes makes it difficult to access short-lived single-molecule events 12 . For example, a comparison of experiments and molecular dynamics (MD) simulations of the well-studied biotin-avidin complex shows that these molecules have a potential to supply forces much larger than that encountered in experiments [13][14][15] . The larger forces will emerge only if bound molecules are pulled apart on a shorter timescale.…”

Probing the Force-Induced Dissociation of Aptamer-Protein Complexes

“…The force dependence of the dissociation of molecular bonds has been extensively described in literature. 17,20,28,29 In accordance with the Bell and Evans model, 17,28 the dissociation rate constant of a molecular bond at zero force, k off (0) (s −1 ), can be related to the change in free energy of the transition state, E b (0), by the following expression:…”

Liaisons « accrocheuses » et mécanique moléculaire

“…En fait, dès 1995, la chambre à flux laminaire permettait de détecter des «complexes de transition» de durée de vie faible au cours de la formation d'une liaison antigène-anticorps [21]. Grâce à une amélioration considérable de sa méthode [22], qui constituait une extension de la microscopie de force atomique, Evan Evans a pu faire varier la «rapidité de mise en charge» (loading rate) des liaisons dans un intervalle extrêmement large, de 10 à 10 5 pN/s: l'analyse des variations de la force de rupture (Figure 2E, F) a permis d'obtenir des détails précis concernant la forme de la courbe «énergie/distance» dans les complexes avidine/biotine [23] …”