Torque generation by one of the motor subunits of heterotrimeric kinesin-2

Abstract

Heterotrimeric kinesin-2 motors [1; 2] transport intraflagellar transport (IFT)-particles from the base to the tip of the axoneme to assemble and maintain cilia [3; 4; 5; 6; 7; 8; 9; 10]. These motors are distinct in containing two non-identical motor subunits together with an accessory subunit [1; 11; 12; 13; 14; 15]. We evaluated the significance of this organization by comparing purified wild type kinesin-2 holoenzymes with mutant trimers containing only one type of motor domain. In motility assays, wild type kinesin-2 moved microtubules (MTs) at a rate intermediate between the rates supported by the two mutants. Interestingly, one of the mutants, but not the other mutant or the wild-type protein, was observed to drive a persistent counter-clockwise rotation of the gliding MTs. Thus one of the two motor domains of heterotrimeric kinesin-2 exerts torque as well as axial force as it moves along a MT, which may allow kinesin-2 to control its circumferential position around a MT doublet within the cilium.

The Kinesin-8 Kip3 Switches Protofilaments in a Sideward Random Walk Asymmetrically Biased by Force

“…For kinesin motors, the ability to bypass obstacles is also an essential property for cargo transport (41)(42)(43). How torque generation (12,13,(18)(19)(20)(21) on the cargo, i.e., a rotation of the cargo around the filament axis, induced by sideward stepping influences cargo transport remains to be seen. Kip3 does not transport cargo but must reach the microtubule end for length regulation.…”

“…Sideward motion of other motors has been detected via rotations of filaments driven by multiple motors in gliding assays and by off-axis movement of motor-attached microspheres or quantum dots used as tracking probes. Probe and microtubule rotations imply torque generation for all cytoskeletal motors: myosin (11), dynein (9,(12)(13)(14)(15)(16)(17) and kinesin (kinesin-1 monomers (18) and dimers (10), kinesin-2 (19,20), kinesin-5 (21), kinesin-8 (16,22), and kinesin-14 (23)). Occasional directed sideward steps-as suggested for kinesin-8-may explain microtubule rotations of motor-ensemble gliding assays (22) or the spiralling motion of multimotor-coated microspheres around microtubules (20).…”

Torque Generation of Kinesin Motors Is Governed by the Stability of the Neck Domain

“…The latest addition to the list of torque-generating kinesins is the heteromeric kinesin (kinesin-2 family) of C. elegans (Pan et al, 2010). Heteromeric kinesins are unique among doubleheaded motors in that they combine two distinct catalytic subunits to generate a functional motor.…”

The Highly Processive Kinesin-8, Kip3, Switches Microtubule Protofilaments with a Bias toward the Left

“…Considering the structure of Eg5 (neck linker length of 18 amino acids (12)), protofilament switching may, however, also be possible during the processive episodes. For kinesin-2 (neck linker length of 17 amino acids, although reduced in length by~5 Å due to proline in cis-conformation at position 13 (12,13)), the propensity to switch protofilaments is controversially discussed and may depend on the stability of the neck domain (11,14).…”