The molecular mechanics of the cell are a frontier that scientists still are striving to learn more about. For example, the cell’s cytoskeleton — which provides structural integrity — is of interest to biologists. The structure arises from actin filaments that assemble into networks and bundles, a process regulated by actin-binding proteins. Scientists don’t understand how the molecular interactions between the actin filaments and the proteins that bind to them regulate cytoskeleton properties. In the July 8, 2008, issue of PNAS, researchers from MIT in Cambridge, Mass., together with investigators from other institutions, report on a single-molecule method to study the strength of interactions between a single actin-binding protein linking two actin filaments. To do so, they immobilized actin filaments on the surface of a flow channel, then introduced an actin-binding protein. One of the filaments was bound to a bead that was then captured in an optical trap. They moved the sample away from the trap using a piezo stage, until the bond between the actin filaments and the actin-binding protein broke. This provided information on the force required to break the interaction. The findings from this experiment supported the hypothesis that both unbinding and unfolding play a significant role in regulating the dynamic behavior of the cytoskeleton.