Nature 537, 107–111 (2016)

In the messy world of the cell, vesicles are the preferred vehicles for intracellular transport. These fluid-filled membrane structures package cargo up and overcome the logistical nightmare of locating, binding and fusing with a target membrane to deliver their goods. But they aren't in it alone. Long, rod-like tethering molecules are tasked with capturing incoming vesicles, then bringing them in to dock. How they achieve this is not fully understood, but the answer might lie in a simple physical mechanism, as David H. Murray and colleagues have now determined.

Using optical tweezers on tethering machinery built from scratch, they found that tether length ranged from the predicted 200 nm, all the way down to an order of magnitude shorter — motivating a hypothesis that a conformational change facilitates docking. They fitted electron microscopy data with the worm-like chain model to determine that the protein charged with regulating recruitment of tethering molecules actually altered their persistence length. The increased flexibility made the out-of-equilibrium conformation of the extended tether vulnerable to entropic collapse, which the authors were able to measure, demonstrating that the tether could function to both capture the vesicle and reel it in.