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Publication: Molecular motors with a gear shift
Dual-speed transport of actin filaments along microtubules
Microtubules and actin filaments are major component of the cytoskeleton. During many cellular processes they function coordinately. Although much of this coordination is mediated by proteins that statically bridge the two cytoskeletal networks, kinesin-14 motors with an actin binding calponin-homology domain (KCHs) have been discovered as potential dynamic cross-linkers in plants. OsKCH1, a KCH from rice, interacts with both microtubules and actin filaments in vivo and in vitro. However, it has remained unclear whether this interaction is dynamic or if actin binding reduces or even abolishes the motor’s motility on microtubules.
The research group of Stefan Diez now directly showed that OsKCH1 is a non-processive, minus end-directed motor which transports actin filaments along microtubules. Interestingly, the authors observed two distinct transport velocities dependent on the relative orientation of the actin filament with respect to the microtubule. In addition, torsional compliance measurements on individual molecules revealed a low flexibility in OsKCH1. The authors suggest that the orientation-dependent transport velocities emerge from OsKCH1's low torsional compliance combined with an inherently oriented binding to the actin filament.
Figure: Model for the mechanism underlying OsKCH1’s two transport velocities. Upper panel: OsKCH1 binds to actin filaments with an inherent orientation. When the actin filament is aligned in its favorable orientation with respect to the microtubule, the transport velocity is not impacted. Lower panel: When the orientation of the actin filament is opposite from the orientation in the upper panel, OsKCH1 molecules need to twist in order to bind to the microtubule. The low torsional compliance of the motor then leads to an impaired binding to the microtubule, resulting in a decreased transport velocity.
W. J. Walter, I. Machens, F. Rafieian, S. Diez: The non-processive rice kinesin-14 OsKCH1 transports actin filaments along microtubules with two distinct velocities, Nature Plants 2015 (in press), DOI: dx.doi.org/10.1038/nplants.2015.111
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