Walking the walk: how kinesin and dynein coordinate their steps
Introduction
Kinesin-1 and cytoplasmic dynein (herein referred to as kinesin and dynein) are two-headed motor proteins that use ATP-derived energy to transport a variety of intracellular cargoes toward the plus-ends and minus-ends of microtubules (MTs), respectively [1, 2]. Kinesin and dynein can take many consecutive steps along their MT tracks without dissociating [3, 4, 5, 6, 7, 8, 9••], allowing them to shuttle cargoes over long distances spanning between a cell's center and periphery. Such continuous movement (termed ‘processivity’) requires head–head coordination to prevent premature MT dissociation and futile cycling of ATP that does not give rise to productive steps. The molecular basis by which one motor domain might ‘sense’ and respond to the nucleotide/conformational state of its identical partner constitutes a major area of study (including processive myosin motors although they are not covered in this review).
A conceptual framework for thinking about intramolecular communication is that one motor domain stalls in a particular mechanochemical intermediate until the partner proceeds through a particular step. This has been coined a ‘gating mechanism’, since one motor domain has to wait until the partner head opens a ‘gate’ that allows it to proceed through the next steps in its mechanochemical cycle. Deciphering the molecular nature of the gate constitutes an important quest for the field. In principle, the gate could operate by controlling the rate at which the motor domain binds or releases from the MT filament (here termed a ‘polymer gate’) or by controlling the rate of a particular chemical transition in the ATPase cycle (here termed a ‘nucleotide gate’). As is true of many regulatory mechanisms in biology, motors may employ more than one type of gating mechanism. There must also be a ‘gatekeeper’ (e.g., a specific conformation of the motor or a chemical transition in the enzymatic site) that controls the opening of the gate. In this review, we first give short and very general overviews of the kinesin and dynein mechanisms. We then discuss recent findings that provide new insights into gating mechanisms that allow the head domains to communicate during processive motion. This topic also has received attention in other recent reviews [10, 11, 12, 13].
Section snippets
Overview of the kinesin mechanism
Kinesin is composed of two identical heavy chains (HCs) and two associated light chains (Figure 1a) [1]. Each HC includes an N-terminal motor domain that houses catalytic activity followed by a coiled-coil stalk that facilitates dimerization. While stepping, ATP hydrolysis is coupled to an 8 nm center-of-mass displacement (Figure 2a) [14, 15], the distance between adjacent tubulin heterodimers. While kinesin predominantly takes forward steps along a single MT protofilament [16, 17, 18••], an
Overview of the dynein mechanism
Unlike kinesin, relatively little is known about the molecular mechanism of dynein (Figure 1b). Dynein, which is a member of the AAA+ family (AAA: ATPase associated with various cellular activities), is involved in diverse processes in eukaryotic cells, such as spindle formation, chromosome segregation, and the trafficking of organelles and mRNA [2]. Dynein is a large protein complex (1.2 MDa) composed of two identical heavy chains and several associated chains [1]. The heavy chain contains six
Potential pathways for head–head communication
A gating mechanism requires that one motor domain can influence the action of its partner. Before we discuss detailed studies for kinesin and dynein, we consider some general models for how this might occur. Possible models for gating are discussed separately in this review. However, many of these mechanisms are not mutually exclusive and it is likely that motors employ more than one gating strategy.
One possibility is that the two motor domains are interacting with one another directly during
Does intramolecular tension facilitate coordination of kinesin's two motor domains?
Most models for tension sensing in head–head communication require that both kinesin heads are bound simultaneously to adjacent tubulin binding sites. In this two-head-bound waiting state, the kinesin neck linker in the front head must extend backward and the neck linker in the rear head must extend forward (Figure 3b). Does such a state exist? The alternating 16 and 0 nm steps observed by single-molecule fluorescence microscopy at rate-limiting ATP concentration [20] are most consistent with a
Coordinating dynein movement
There is general agreement that dynein moves processively [5, 6, 7, 8, 9••, 33, 54, 55] but the underlying mechanism remains unknown. Some form of interhead coordination must exist in dynein, since dynein processivity requires two heads [8, 32]. Furthermore, a truncated single-headed dynein spends less time MT-attached during its ATPase cycle than a head of a walking two-headed dynein [32], suggesting that mechanochemical steps in one head are affected by the presence of the second head. Hence,
Conclusions
Single-molecule and ensemble-based kinetic experiments have provided evidence that the structural elements that interconnect the two motor domains (neck linkers for kinesin and unknown structural linker elements in the case of dynein) are crucial for head–head coordination. These structural elements are under tension in case of kinesin, allowing a very tight coupling between ATP hydrolysis and forward stepping. The connection between the heads may be ‘more flexible’ for dynein, resulting in
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
• of special interest
•• of outstanding interest
Acknowledgements
The authors would like to thank Nick Guydosh and Michael Diehl for helpful comments on the manuscript.
References (60)
The molecular motor toolbox for intracellular transport
Cell
(2003)- et al.
Single cytoplasmic dynein molecule movements: characterization and comparison with kinesin
Biophys J
(1995) - et al.
Single-molecule analysis of dynein processivity and stepping behavior
Cell
(2006) - et al.
Force-induced bidirectional stepping of cytoplasmic dynein
Cell
(2007) - et al.
Kinesin's moonwalk
Curr Opin Cell Biol
(2006) Kinesin motor mechanics: binding, stepping, tracking, gating, and limping
Biophys J
(2007)- et al.
To step or not to step? How biochemistry and mechanics influence processivity in Kinesin and Eg5
Curr Opin Cell Biol
(2007) - et al.
Kinesin hydrolyses one ATP per 8-nm step
Nature
(1997) - et al.
Mechanics of the kinesin step
Nature
(2005) - et al.
Nucleotide-induced conformations in the neck region of dimeric kinesin
EMBO J
(2003)
Single-molecule observations of neck linker conformational changes in the kinesin motor protein
Nat Struct Mol Biol
Distinct functions of nucleotide-binding/hydrolysis sites in the four AAA modules of cytoplasmic dynein
Biochemistry
ATP hydrolysis cycle-dependent tail motions in cytoplasmic dynein
Nat Struct Mol Biol
Kinesin-microtubule binding depends on both nucleotide state and loading direction
Proc Natl Acad Sci U S A
3D structure of eukaryotic flagella in a quiescent state revealed by cryo-electron tomography
Proc Natl Acad Sci U S A
Kinesin and dynein–dynactin at intersecting microtubules: motor density affects dynein function
Biophys J
Dynein: an ancient motor protein involved in multiple modes of transport
J Neurobiol
Movement of microtubules by single kinesin molecules
Nature
Bead movement by single kinesin molecules studied with optical tweezers
Nature
Cytoplasmic dynein functions as a gear in response to load
Nature
Overlapping hand-over-hand mechanism of single molecular motility of cytoplasmic dynein
Proc Natl Acad Sci U S A
Kinesin: world's tiniest biped
Curr Opin Cell Biol
Coupling of kinesin steps to ATP hydrolysis
Nature
A model for kinesin movement from nanometer-level movements of kinesin and cytoplasmic dynein and force measurements
J Cell Sci Suppl
Kinesin follows the microtubule's protofilament axis
J Cell Biol
Intramolecular strain coordinates kinesin stepping behavior along microtubules
Cell
Kinesin walks hand-over-hand
Science
A structural change in the kinesin motor protein that drives motility
Nature
Force generation in kinesin hinges on cover-neck bundle formation
Structure
ATP reorients the neck linker of kinesin in two sequential steps
J Biol Chem
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