Cytoplasmic Dynein Moves Through Uncoordinated Stepping of the AAA+ Ring Domains

Abstract

Cytoplasmic dynein is a homodimeric AAA+ motor that transports a multitude of cargos toward the microtubule minus end. How the two catalytic head domains interact and move relative to each other during processive movement is unclear. Here, we tracked the relative positions of both heads with nanometer precision and directly observed the heads moving independently along the microtubule. The heads remained widely separated, and their stepping behavior varied as a function of interhead separation. One active head was sufficient for processive movement, and an active head could drag an inactive partner head forward. Thus, dynein moves processively without interhead coordination, a mechanism fundamentally distinct from the hand-over-hand stepping of kinesin and myosin.

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

“…For axonemal dynein motors, off-axis movement-causing microtubule rotations and, thus, torque-may be important for the three-dimensional motion of the flagellar beat (12,13); for cytoplasmic dynein, sideward steps may be an essential biological requirement such that heads can pass each other, obstacles, or counter-propagating kinesin motors (15)(16)(17)40). For kinesin motors, the ability to bypass obstacles is also an essential property for cargo transport (41)(42)(43).…”

“…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).…”

“…However, motors may also randomly switch protofilaments with a bias toward one direction, resulting in the same net ensemble motion. Although data on single cytoplasmic dyneins suggest a diffusive, i.e., undirected, sideward stepping mechanism (15)(16)(17), the switching mechanism of single kinesin motors remains poorly understood. In both cases, how sideward stepping may depend on load is unclear.…”

Cytoplasmic dynein regulates its attachment to microtubules via nucleotide state-switched mechanosensing at multiple AAA domains

“…The farther apart its heads are spread on the MT (i.e., the greater the intramolecular tension), the shorter the dwell time before the next step and the greater the probability of the rear head advancing (12,13). We demonstrated ATP-independent, force-induced bidirectional stepping by dynein in which the motor moves processively under the constant force of an optical trap.…”

“…For dynein to "walk," one motor domain ("head") must remain MT-bound while the other moves (10)(11)(12)(13), thus requiring coordination of the "internal" cycles of both heads. Dynein may use allosteric mechanosensing (possibly through the stalk) to differentiate between the leading and trailing heads, because they experience oppositely directed mechanical tension (Fig.…”