Force-clamp spectroscopy of reversible bond breakage

Abstract

We consider reversible breaking of adhesion bonds or folding of proteins under the influence of a constant external force. We discuss the statistical properties of the unbinding/rebinding events and analyze their mean number and their variance in the framework of simple kinetic models. In the calculations, we explicitly exploit the analogy to single molecule fluorescence and particularly between unbinding/rebinding and photon emission events. Whereas for two-state behavior Poisson or sub-Poisson statistics of the events is found, we show that for more general kinetic schemes also super-Poisson statistics can occur. Temporal fluctuations of the transition rates, a hallmark for the presence of dynamic disorder, should become experimentally accessible via the determination of the second moment of the event-number distribution. © 2009 American Institute of Physics.