Force Spectroscopy and Dynamics of the BiotinAvidin Bond Studied by Scanning Force Microscopy

Scanning force microscopy (SFM) has been used to measure the strength of bonds between biological receptor molecules and their ligands. Here we report the measurement of the unbinding forces between avidin and biotin a model of the receptor-ligand interactions used in earlier studies- as a function of the loading rate. We have explored the unbinding force over three orders of magnitude in loading rate, and find that the force increases from ∼20 pN to ∼80 pN with increasing loading rate. We argue that the unbinding forces are connected to the bond lifetime as a function of an applied force. This allows to estimate thermal off-rates from measurements at finite forces. The deduced behavior of the bond lifetime of avidin-biotin in dependence of the force indicates that the dissociation proceeds via an intermediate state. Our data thus also allows to estimate the rate of an intermediate transition of the dissociation process.