A Force Dependent Gating Mechanism Inhibits ATP Dependent Release of Dynein from Microtubules

Abstract

Cytoplasmic dynein is a processive minus end directed microtubule motor involved in a wide range of cellular functions. By studying how dynein monomers respond to load in an optical trapping assay, we discovered a force dependent gating mechanism that prevents ATP driven release of dynein from the microtubule. Our results show that tension on dynein's linker domain causes the microtubule release rate of the motor to be insensitive to ATP, while dynein motors with an unloaded linker release at a much faster rate at high ATP concentrations. We found that dynein monomers preferentially release when force is applied towards the minus end of the microtubule rather than the plus end. This strong asymmetry is observed even in the absence of dynein's ATPase ring, implying it is an intrinsic property of the stalk and microtubule binding domain. To test what role these phenomena play in dynein motility, we studied ATPase mutants with altered translocation velocities and measured their force dependent release kinetics. On the basis of these results we developed a minimal model of dynein motility and show how intramolecular tension, powerstroke and force dependent release are main determinants of dynein's motility properties and directionality.