Kinesin motor activation: microtubules pull the switches

摘要

Within the teeming interior of the cell, many molecular machines drive the essential processes of life. These nanomachines use cellular fuel—ATP—and, as also ought to be true for everyday macromachines, fuel efficiency is paramount. Thus the cell’s nanomachines have evolved to use ATP only when they can couple it to essential work. A study published in PNAS (1) provides unprecedented detail of how one family of cytoskeleton-based nanomachines—the microtubule-tracking kinesins—achieves such fuel efficiency. Kinesin superfamily members undertake a wide variety of microtubule (MT)-related tasks, including movement in either direction along their polar MT tracks and regulation of MT dynamics (2). Central to these diverse cellular functions, however, is a highly conserved mechanism for binding MTs and ATP by the kinesin motor domain. MT binding stimulates the kinesin ATPase by several orders of magnitude, and coupling between high-/low-affinity MT binding (for motor recycling) and the energy-providing ATPase activity lies at the heart of motor efficiency (3). This coupling is ultimately used to transmit force to the motors’ binding partners, but the precise structural basis for all these steps is the subject of ongoing research. Many strands of biophysical evidence have defined the chemical and mechanical features of the kinesin machine (4), whereas structural biology approaches have enabled direct visualization of the motor engine components.