A molecular motor finds its track

Review: Mechanochemistry of the kinesin-1 ATPase

Kinesins are P‐loop NTPases that can do mechanical work. Like small G‐proteins, to which they are related, kinesins execute a program of active site conformational changes that cleaves the terminal phosphate from an NTP substrate. But unlike small G‐proteins, kinesins can amplify and harness these conformational changes in order to exert force. In this short review I summarize current ideas about how the kinesin active site works and outline how the active site chemistry is coupled to the larger‐scale structural cycle of the kinesin motor domain. Focusing largely on kinesin‐1, the best‐studied kinesin, I discuss how the active site switch machinery of kinesin cycles between three distinct states, how docking of the neck linker stabilizes two of these states, and how tension‐sensitive and position‐sensitive neck linker docking may modulate both the hydrolysis step of ATP turnover and the trapping of product ADP in the active site. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 476–482, 2016.

Allosteric control of kinesin's motor domain by tubulin: a molecular dynamics study

Molecular motors such as kinesin are essential for many biological processes. These motors have two motor domains, which bind to tubulin filaments, hydrolyze ATP, and transduce the released chemical energy into directed movements. The general principles of this chemomechanical coupling are now well-established but the underlying molecular mechanisms remain elusive because small conformational changes within large proteins are difficult to detect experimentally. Here, we use atomistic molecular dynamics simulations to monitor such changes within a single motor domain of KIF1A, which belongs to the kinesin-3 motor family. The nucleotide binding pocket of this domain can be empty or occupied by ATP or ADP. For these three nucleotide states, we determine the mobility of the backbone of the protein, both in solution and attached to tubulin. Only one subdomain of the motor domain is found to exhibit a strongly increased mobility upon binding to tubulin: the neck linker that presumably acts as a mechanical transmitter to the other motor domain in dimeric kinesin-3 motors. Furthermore, upon binding to tubulin, the neck linker mobility becomes sensitive to the bound nucleotide and is highly increased after phosphate release, which implies undocking of this linker from the core of the motor domain. These simulation results are consistent with experimental data from EPR spectroscopy, FRET, and cryo-electron microscopy. A detailed analysis of our simulation data also reveals that the undocking of the neck linker in the ADP-kinesin-tubulin state arises from allosteric interactions between the nucleotide and tubulin and that the β-sheet core undergoes a twist both during phosphate release and ATP binding. The computational approach used here can be applied to other motor domains and mechanoenzymes in order to identify allosteric interactions between the subdomains of these proteins.

KIF14 binds tightly to microtubules and adopts a rigor-like conformation

The mitotic kinesin motor protein KIF14 is essential for cytokinesis during cell division and has been implicated in cerebral development and a variety of human cancers. Here we show that the mouse KIF14 motor domain binds tightly to microtubules and does not display typical nucleotide-dependent changes in this affinity. It also has robust ATPase activity but very slow motility. A crystal structure of the ADP-bound form of the KIF14 motor domain reveals a dramatically opened ATP-binding pocket, as if ready to exchange its bound ADP for Mg·ATP. In this state, the central β-sheet is twisted ~10° beyond the maximal amount observed in other kinesins. This configuration has only been seen in the nucleotide-free states of myosins-known as the "rigor-like" state. Fitting of this atomic model to electron density maps from cryo-electron microscopy indicates a distinct binding configuration of the motor domain to microtubules. We postulate that these properties of KIF14 are well suited for stabilizing midbody microtubules during cytokinesis.