- Open Access
Eg5 steps it up!
© Valentine et al; licensee BioMed Central Ltd. 2006
- Received: 06 December 2006
- Accepted: 15 December 2006
- Published: 15 December 2006
Understanding how molecular motors generate force and move microtubules in mitosis is essential to understanding the physical mechanism of cell division. Recent measurements have shown that one mitotic kinesin superfamily member, Eg5, is mechanically processive and capable of crosslinking and sliding microtubules in vitro. In this review, we highlight recent work that explores how Eg5 functions under load, with an emphasis on the nanomechanical properties of single enzymes.
- Motor Domain
- Motor Head
- Kinesin Family Member
- Spindle Matrix
- Conventional Kinesin
Eg5 motors slide microtubules during cell division
During metaphase, the mitotic spindle maintains constant size and shape despite poleward movement of microtubules that is coupled to minus-end disassembly at the spindle pole, a process known as "poleward flux" [8, 9]. The mechanism driving poleward translocation remains controversial, but likely involves both microtubule polymerization in the mid-zone as well as motor-mediated microtubule sliding [10–12].
The tetrameric structure of Eg5 makes it a particularly attractive candidate for binding antiparallel microtubules and sliding them apart [13, 14]. However, dissecting the role of Eg5 in poleward flux is challenging, since its selective removal or inhibition often leads to serious mitotic defects. In Xenopus egg extracts, experiments are tractable as it is possible to stabilize bipolar spindles while monitoring the movement of microtubules using fluorescence speckle microscopy [11, 15]. Such experiments have indicated that Eg5 is required for poleward translocation of spindle microtubules . Moreover, biochemical depletion of Eg5 significantly decreases flux rate, and pharmacological inhibition of Eg5 produces a dose-dependent slowing . Flux persists in spindles in which microtubule depolymerization has been blocked through chemical treatment by hexylene glycol or the addition of pole-disrupting reagents, providing further evidence that Eg5-mediated sliding, and not depolymerization, dominates flux generation in egg extracts [16, 17].
While Eg5 may be essential for generating flux in Xenopu s-derived spindles, where flux is fast relative to chromosome movement, its role in higher eukaryotes, where flux is relatively slow, is less clear [18, 19]. Inhibition of Eg5 in mammalian PtK1 cells results in only a minor reduction in the flux rate, suggesting that depolymerization may be more important in this system . Consistent with this, depletion of the Kinesin-13 subfamily depolymerizing proteins KIF2A and MCAK in human U2OS cells eliminated poleward flux and reduced poleward chromosome velocity at anaphase, albeit with no deleterious effect on overall mitotic progression . Flux rates vary significantly among different cell types and between mitotic and meiotic systems, suggesting there may not be a single dominant mechanism or function for poleward flux in all cells [8, 18, 21].
Establishing Eg5 processivity is critical to understanding its function
Intriguingly, the distribution of Eg5 in Xenopus egg extracts is static with respect to poleward-fluxing microtubules. Two competing models have been proposed to explain this effect. In the first, ensembles of Eg5 motors transiently bind to a microtubule, stroke, and detach, thereby pushing microtubules poleward without maintaining prolonged contact with the tubulin substrate. To prevent diffusion away from the spindle, Eg5 motors are proposed to interact with a non-microtubule-based matrix in the spindle [22–24]. Although the molecular identity of the proposed "spindle matrix" is unknown, several candidate filaments are required for spindle function, including the nuclear/mitotic apparatus protein (NuMA) , lamin-B , and the branched polyelectrolyte, poly(ADP-ribose) . Alternatively, if Eg5 tetramers are mechanically processive, taking multiple steps along the microtubule before detaching, they could simultaneously move towards the plus ends of the two antiparallel microtubules they crosslink . This would slide both microtubules toward opposing poles while the Eg5 motors remained stationary, as if walking on juxtaposed treadmills.
The key distinction between these models is the amount of time Eg5 motors remain bound to the microtubule during the kinetic cycle. Early solution biochemistry experiments sought to resolve this controversy by measuring the "chemical processivity", or the number of ATP molecules consumed per diffusional encounter with the microtubule, which scales with the ratio of the rate of catalysis, k cat, to the equilibrium binding constant, K 50%MTs . Dimeric Xenopus-derived truncation mutants were found to be less chemically processive than either kinesin monomers or ncd dimers, both of which are known to be mechanically nonprocessive. From these data, it was concluded that Eg5 is "slightly if at all processive." The dose-responsive hyperbolic slowing of flux in response to pharmacological inhibition of Eg5  – resembling the slowing of gliding actin filaments when the number of driving nonprocessive myosin motors is reduced- was taken as further evidence of nonprocessivity . Although these data have been widely interpreted as evidence of nonprocessivity, a lack of mechanical data precluded a definitive determination.
In light of these single-molecule experiments, previous conclusions of Eg5 nonprocessivity must be reconsidered. Chemical processivity measurements should never be mistaken as evidence of true mechanically-processive movement , and may be particularly poor estimators for motors with small run lengths. The hyperbolic slowing of Eg5-driven flux as a function of inhibitor concentration that was initially interpreted as evidence of nonprocessivity may instead indicate that inhibited motors remain weakly associated with microtubules, acting as a brake [33, 35, 36]. Further experiments investigating the mechanical basis of inhibition will be required to fully understand this result. While Eg5's mechanical processivity and ability to crosslink and slide microtubules in vitro certainly does not rule out the presence of a static spindle matrix, the immobilization of Eg5 within the spindle can no longer be used as evidence supporting its existence.
Eg5's load-dependent mechanochemistry shows key distinctions as compared to conventional kinesin
Establishing that Eg5 is a processive enzyme not only sheds new light on its physiological role, but readily allows measurement of some of the most interesting and informative motor properties: the force-velocity relationship and stall force. Taken together, the mechanical properties of Eg5 show several important distinctions from those of conventional kinesin, a cargo transporter. Through a comparative analysis we may begin to gain insight into how physiology influences motor function, and how small changes in protein structure or organization give rise to the distinct mechanical properties of all kinesin family members.
Both Eg5 and kinesin velocities display a Michaelis-Menten dependence on ATP concentration, but the overall velocity of Eg5 is significantly slower, with a maximal stepping rate of 100 nm/s, compared to approximately 650 nm/s for conventional kinesin [30, 37]. Eg5 is also much less processive, taking ~8 steps at a time at saturating ATP and zero load, while kinesin takes 50 steps or more under similar conditions [30, 38].
Structural differences may be responsible for unusual force response
Several recent studies have revealed structural properties that could contribute to Eg5's unique mechanochemical characteristics. The crystal structure of the motor domain for a human-derived Eg5 monomer bound to ADP showed a novel, ordered neck linker configuration that is docked perpendicular to the long edge of the protein via a series of hydrogen bonds . In all previous kinesin family member structures, the neck linker was either disordered or docked parallel to the long edge of the protein, and in the ADP-bound state, the neck linker is typically floppy [42–45]. The residues involved in Eg5's novel docking are highly conserved among Kinesin-5 family members, suggesting that this conformation may be specific to this subclass of motors .
Although a rigid neck linker would impart molecular stiffness, perhaps allowing controlled microtubule sliding under constant tension, it could also hinder each motor head's diffusional search for the next tubulin binding site. A unique mode of motility might provide a much-needed mechanical compromise, allowing processive motion under significant load even with an inflexible neck linker. Based on a series of ensemble FRET measurements, Rosenfeld, et al. proposed three different rigid neck linker conformations for the ATP-, ADP- and no nucleotide-bound states, and further showed that Eg5 likely moves in two sequential steps . First, ATP binding docks the neck linker parallel to the motor domain, then, upon hydrolysis, the entire motor domain rolls forward along the microtubule. This two-step mode of motility could be critical for Eg5 function and may influence its relative insensitivity to applied force.
Interestingly, a recent report indicates that full-length GFP-tagged Eg5 motors display an unusual mode of motility: processive directional movement interrupted by periods of diffusion as tetramers move along a single coverslip-bound microtubule . One-dimensional diffusion along the tubulin lattice has been reported for other kinesin-related proteins such as monomeric KIF1A [47, 48] and MCAK, a centromere-associated depolymerizer ; localization arises from the electrostatic attraction of the motor to the highly negatively-charged microtubule. Further experiments will be required to determine the role of electrostatic interactions in Eg5, to demonstrate whether the diffusive state is specific to tetrameric motors moving along an isolated microtubule or exists for dimers or tetramers bridging two microtubules, and to determine how much force motors undergoing diffusion can withstand before they detach. This diffusive mode could be important to Eg5's function by increasing the total time each motor remains localized to the spindle and therefore the likelihood that tetramers will form crosslinks in cells.
Coordination within and among Eg5 motors
Some of the biggest questions about Eg5 motility surround coordination: Do individual Eg5 dimers move by a hand-over-hand mechanism, like conventional kinesin does [50–52]? Are the four motor heads of single Eg5 tetramers coordinated? Finally, do ensembles of Eg5 motors work together to generate force in cell division, and how is the force generated by Eg5 motors balanced against forces generated by other spindle motors (such as ncd, dynein, and the chromokinesins) [53–55]?
Conventional kinesin likely works in isolation to tote cargo long distances in cells. Such highly processive movement requires that the catalytic cycles of the two motor heads be tightly coordinated to prevent simultaneous dissociation. It is proposed that intramolecular strain transmitted by the neck linker regulates the biochemical state of each motor head, keeping the two heads biochemically out-of-phase and allowing one head to maintain a tight grip on the microtubule at all times, even under considerable load [56–58].
By contrast, Eg5 probably works in small ensembles. The limited processivity of Eg5 may arise because ensembles of motors must work together within the spindle. By taking multiple steps, single motors maintain sustained contact with their microtubule substrates and aid in de novo spindle assembly. By dissociating quickly, however, motors detach from the microtubule before stalling and slowing other motors in the ensemble, promoting efficient sliding once spindles are formed. These short run lengths may prove to be a consequence of reduced head-head coordination resulting from the rigid nature of the neck linker. Additional experiments will be required to unravel the extent of catalytic coordination, and determine if Eg5 dimers walk hand-over-hand.
In native tetramers, another level of coordination is possible: the opposing pairs of motors heads located at either end of the coiled-coil stalk could cooperate to enhance processivity. Based on the average run length for the dimer, and assuming each pair of dimers in the homotetramer moves independently, the tetramer should remain attached to the spindle for ~64 steps, on average . This simple model would predict a run length of ~520 nm, surprisingly similar to the ~580-nm average run length of GFP-Eg5 tetramers moving along a single microtubule in vitro . In principle, either linear or torsional strain within the extended stalk domain could allow the pairs of dimers to communicate, thereby modulating tetrameric run lengths. Direct mechanical measurements of single full-length Eg5 tetramers moving on two microtubules will be necessary to probe this possibility. Finally, new in vitro assays capable of measuring the forces exerted by ensembles of motors are required to fully understand how mixed populations of motors work together to organize and move microtubules in cells.
Single-molecule measurements of the motor proteins that generate force during mitosis are indispensable for elucidating the physical basis of cell division. Establishing whether or not these motors are processive and how they respond to force is critical to developing predictive computational models and to understanding how ensembles of motors cooperate to balance forces during each stage of division. Although many mitotic motor proteins have been identified, little nanomechanical characterization has been performed and many important questions remain. The new in vitro assays [13, 30] reviewed here should allow complete characterization of Kinesin-5 subclass members, as well as rapid expansion into new classes of motor proteins. These new data will permit unprecedented comparative studies of diverse kinesin family members and shed new light on both how protein structure influences motor function and how biochemical energy is harnessed into productive work by all mechanoenzymes.
This work was supported by grants to S.M.B. from the National Institutes of Health (NIH). M.T.V. was supported by a Career Award at the Scientific Interface from the Burroughs Wellcome Fund. P.M.F. was supported by a predoctoral fellowship from the National Science Foundation (NSF) and a Lieberman fellowship. We thank Susan Gilbert, Steve Rosenfeld, Duane Compton and members of the Block lab for helpful discussions, and in particular, Jennifer Shanoski and Nick Guydosh for careful reading of the manuscript.
- Cole DG, Saxton WM, Sheehan KB, Scholey JM: A "slow" homotetrameric kinesin-related motor protein purified from Drosophila embryos. J Biol Chem 1994,269(37):22913–22916.PubMed CentralPubMedGoogle Scholar
- Sawin KE, LeGuellec K, Philippe M, Mitchison TJ: Mitotic spindle organization by a plus-end-directed microtubule motor. Nature 1992,359(6395):540–543. 10.1038/359540a0PubMedView ArticleGoogle Scholar
- Wittmann T, Hyman A, Desai A: The spindle: a dynamic assembly of microtubules and motors. Nat Cell Biol 2001, 3: E28-E34. 10.1038/35050669PubMedView ArticleGoogle Scholar
- Hagan I, Yanagida M: Kinesin-related cut 7 protein associates with mitotic and meiotic spindles in fission yeast. Nature 1992,356(6364):74–76. 10.1038/356074a0PubMedView ArticleGoogle Scholar
- Le Guellec R, Paris J, Couturier A, Roghi C, Philippe M: Cloning by differential screening of a Xenopus cDNA that encodes a kinesin-related protein. Mol Cell Biol 1991,11(6):3395–3398.PubMed CentralPubMedView ArticleGoogle Scholar
- Heck MM, Pereira A, Pesavento P, Yannoni Y, Spradling AC, Goldstein LS: The kinesin-like protein KLP61F is essential for mitosis in Drosophila. J Cell Biol 1993,123(3):665–679. 10.1083/jcb.123.3.665PubMedView ArticleGoogle Scholar
- Blangy A, Lane HA, d'Herin P, Harper M, Kress M, Nigg EA: Phosphorylation by p34cdc2 regulates spindle association of human Eg5, a kinesin-related motor essential for bipolar spindle formation in vivo. Cell 1995,83(7):1159–1169. 10.1016/0092-8674(95)90142-6PubMedView ArticleGoogle Scholar
- Rogers GC, Rogers SL, Sharp DJ: Spindle microtubules in flux. J Cell Sci 2005,118(6):1105–1116. 10.1242/jcs.02284PubMedView ArticleGoogle Scholar
- Maddox P, Straight A, Coughlin P, Mitchison TJ, Salmon ED: Direct observation of microtubule dynamics at kinetochores in Xenopus extract spindles: implications for spindle mechanics. J Cell Biol 2003,162(3):377–382. 10.1083/jcb.200301088PubMed CentralPubMedView ArticleGoogle Scholar
- Sawin KE, Mitchison TJ: Poleward microtubule flux mitotic spindles assembled in vitro. J Cell Biol 1991,112(5):941–954. 10.1083/jcb.112.5.941PubMedView ArticleGoogle Scholar
- Miyamoto DT, Perlman ZE, Burbank KS, Groen AC, Mitchison TJ: The kinesin Eg5 drives poleward microtubule flux in Xenopus laevis egg extract spindles. J Cell Biol 2004,167(5):813–818. 10.1083/jcb.200407126PubMed CentralPubMedView ArticleGoogle Scholar
- Rogers GC, Rogers SL, Schwimmer TA, Ems-McClung SC, Walczak CE, Vale RD, Scholey JM, Sharp DJ: Two mitotic kinesins cooperate to drive sister chromatid separation during anaphase. Nature 2004,427(6972):364–370. 10.1038/nature02256PubMedView ArticleGoogle Scholar
- Kapitein LC, Peterman EJG, Kwok BH, Kim JH, Kapoor TM, Schmidt CF: The bipolar mitotic kinesin Eg5 moves on both microtubules that it crosslinks. Nature 2005,435(7038):114–118. 10.1038/nature03503PubMedView ArticleGoogle Scholar
- Sharp DJ, McDonald KL, Brown HM, Matthies HJ, Walczak C, Vale RD, Mitchison TJ, Scholey JM: The bipolar kinesin, KLP61F, cross-links microtubules within interpolar microtubule bundles of Drosophila embryonic mitotic spindles. J Cell Biol 1999,144(1):125–138. 10.1083/jcb.144.1.125PubMed CentralPubMedView ArticleGoogle Scholar
- Waterman-Storer CM, Desai A, Bulinski JC, Salmon ED: Fluorescent speckle microscopy, a method to visualize the dynamics of protein assemblies in living cells. Curr Biol 1998,8(22):1227–1230. 10.1016/S0960-9822(07)00515-5PubMedView ArticleGoogle Scholar
- Shirasu-Hiza M, Perlman ZE, Wittmann T, Karsenti E, Mitchison TJ: Eg5 causes elongation of meiotic spindles when flux-associated microtubule depolymerization is blocked. Curr Biol 2004,14(21):1941–1945. 10.1016/j.cub.2004.10.029PubMedView ArticleGoogle Scholar
- Mitchison TJ: Mechanism and function of poleward flux in Xenopus extract meiotic spindles. Philos Trans R Soc Lond B Biol Sci 2005,360(1455):623–629. 10.1098/rstb.2004.1616PubMed CentralPubMedView ArticleGoogle Scholar
- Ganem NJ, Compton DA: Functional roles of poleward microtubule flux during mitosis. Cell Cycle 2006,5(5):481–485.PubMedView ArticleGoogle Scholar
- Ganem NJ, Upton K, Compton DA: Efficient mitosis in human cells lacking poleward microtubule flux. Curr Biol 2005, 15: 1827–1832. 10.1016/j.cub.2005.08.065PubMedView ArticleGoogle Scholar
- Cameron LA, Yang G, Cimini D, Canman JC, Kisurina-Evgenieva O, Khodjakov A, Danuser G, Salmon ED: Kinesin 5-independent poleward flux of kinetochore microtubules in PtK1 cells. J Cell Biol 2006,173(2):173–179. 10.1083/jcb.200601075PubMed CentralPubMedView ArticleGoogle Scholar
- Maddox P, Desai A, Oegema K, Mitchison TJ, Salmon ED: Poleward microtubule flux is a major component of spindle dynamics and anaphase a in mitotic Drosophila embryos. Curr Biol 2002,12(19):1670–1674. 10.1016/S0960-9822(02)01183-1PubMedView ArticleGoogle Scholar
- Kapoor TM, Mitchison TJ: Eg5 is static in bipolar spindles relative to tubulin: evidence for a static spindle matrix. J Cell Biol 2001,154(6):1125–1134. 10.1083/jcb.200106011PubMed CentralPubMedView ArticleGoogle Scholar
- Scholey JM, Rogers GC, Sharp DJ: Mitosis, microtubules, and the matrix. J Cell Biol 2001,154(2):261–266. 10.1083/jcb.200101097PubMed CentralPubMedView ArticleGoogle Scholar
- Wells WA: Searching for a spindle matrix. J Cell Biol 2001,154(6):1102–1104. 10.1083/jcb.200108139PubMed CentralPubMedView ArticleGoogle Scholar
- Dionne MA, Howard L, Compton DA: NuMA is a component of an insoluble matrix at mitotic spindle poles. Cell Motil Cytoskeleton 1999,42(3):189–203. 10.1002/(SICI)1097-0169(1999)42:3<189::AID-CM3>3.0.CO;2-XPubMedView ArticleGoogle Scholar
- Tsai MY, Wang S, Heidinger JM, Shumaker DK, Adam SA, Goldman RD, Zheng Y: A mitotic lamin B matrix Induced by RanGTP required for spindle assembly. Science 2006,311(5769):1887–1893. 10.1126/science.1122771PubMedView ArticleGoogle Scholar
- Chang P, Jacobson MK, Mitchison TJ: Poly(ADP-ribose) is required for spindle assembly and structure. Nature 2004,432(7017):645–649. 10.1038/nature03061PubMedView ArticleGoogle Scholar
- Crevel IMTC, Lockhart A, Cross RA: Kinetic evidence for low chemical processivity in ncd and Eg5. J Mol Biol 1997,273(1):160–170. 10.1006/jmbi.1997.1319PubMedView ArticleGoogle Scholar
- Uyeda TQP, Kron SJ, Spudich JA: Myosin step size : Estimation from slow sliding movement of actin over low densities of heavy meromyosin. J Mol Biol 1990,214(3):699–710. 10.1016/0022-2836(90)90287-VPubMedView ArticleGoogle Scholar
- Valentine MT, Fordyce PM, Krzysiak TC, Gilbert SP, Block SM: Individual dimers of the mitotic kinesin motor Eg5 step processively and support substantial loads in vitro. Nat Cell Biol 2006,8(5):470–476. 10.1038/ncb1394PubMed CentralPubMedView ArticleGoogle Scholar
- deCastro MJ, Fondecave RM, Clarke LA, Schmidt CF, Stewart RJ: Working strokes by single molecules of the kinesin-related microtubule motor ncd. Nat Cell Biol 2000,2(10):724–729. 10.1038/35036357PubMedView ArticleGoogle Scholar
- deCastro MJ, Ho CH, Stewart RJ: Motility of dimeric ncd on a metal-chelating surfactant: Evidence that ncd Is not processive. Biochemistry 1999,38(16):5076–5081. 10.1021/bi9829175PubMedView ArticleGoogle Scholar
- Kwok BH, Kapitein LC, Kim JH, Peterman EJG, Schmidt CF, Kapoor TM: Allosteric inhibition of kinesin-5 modulates its processive directional motility. Nat Chem Biol 2006,2(9):480–5. 10.1038/nchembio812PubMedView ArticleGoogle Scholar
- Jiang W, Hackney DD: Monomeric kinesin head domains hydrolyze multiple ATP molecules before release from a microtubule. J Biol Chem 1997,272(9):5616–5621. 10.1074/jbc.272.9.5375PubMedView ArticleGoogle Scholar
- Crevel IMTC, Alonso MC, Cross RA: Monastrol stabilises an attached low-friction mode of Eg5. Curr Biol 2004,14(11):R411–412. 10.1016/j.cub.2004.05.030PubMedView ArticleGoogle Scholar
- Krzysiak TC, Wendt T, Sproul LR, Tittmann P, Gross H, Gilbert SP, Hoenger A: A structural model for monastrol inhibition of dimeric kinesin Eg5. EMBO J 2006, 25: 2263–2273. 10.1038/sj.emboj.7601108PubMed CentralPubMedView ArticleGoogle Scholar
- Block SM, Asbury CL, Shaevitz JW, Lang MJ: Probing the kinesin reaction cycle with a 2D optical force clamp. Proc Natl Acad Sci U S A 2003,100(5):2351–2356. 10.1073/pnas.0436709100PubMed CentralPubMedView ArticleGoogle Scholar
- Block SM, Goldstein LS, Schnapp BJ: Bead movement by single kinesin molecules studied with optical tweezers. Nature 1990,348(6299):348–352. 10.1038/348348a0PubMedView ArticleGoogle Scholar
- Carter NJ, Cross RA: Mechanics of the kinesin step. Nature 2005,435(7040):308–312. 10.1038/nature03528PubMedView ArticleGoogle Scholar
- Block SM: Nanometres and piconewtons: the macromolecular mechanics of kinesin. Trends Cell Biol 1995,5(4):169–175. 10.1016/S0962-8924(00)88982-5PubMedView ArticleGoogle Scholar
- Turner J, Anderson R, Guo J, Beraud C, Fletterick R, Sakowicz R: Crystal structure of the mitotic spindle kinesin Eg5 reveals a novel conformation of the neck-linker. J Biol Chem 2001,276(27):25496–25502. 10.1074/jbc.M100395200PubMedView ArticleGoogle Scholar
- Nitta R, Kikkawa M, Okada Y, Hirokawa N: KIF1A alternately uses two loops to bind microtubules. Science 2004,305(5684):678–683. 10.1126/science.1096621PubMedView ArticleGoogle Scholar
- Kikkawa M, Sablin EP, Okada Y, Yajima H, Fletterick RJ, Hirokawa N: Switch-based mechanism of kinesin motors. Nature 2001,411(6836):439–445. 10.1038/35078000PubMedView ArticleGoogle Scholar
- Kull FJ, Sablin EP, Lau R, Fletterick RJ, Vale RD: Crystal structure of the kinesin motor domain reveals a structural similarity to myosin. Nature 1996,380(6574):550–555. 10.1038/380550a0PubMed CentralPubMedView ArticleGoogle Scholar
- Sablin EP, Kull FJ, Cooke R, Vale RD, Fletterick RJ: Crystal structure of the motor domain of the kinesin-related motor ncd. Nature 1996,380(6574):555–559. 10.1038/380555a0PubMedView ArticleGoogle Scholar
- Rosenfeld SS, Xing J, Jefferson GM, King PH: Docking and rolling--a model of how the mitotic motor Eg5 works. J Biol Chem 2005,280(42):35684–35695. 10.1074/jbc.M506561200PubMedView ArticleGoogle Scholar
- Okada Y, Hirokawa N: A processive single-headed motor: Kinesin superfamily protein KIF1A. Science 1999,283(5405):1152–1157. 10.1126/science.283.5405.1152PubMedView ArticleGoogle Scholar
- Okada Y, Hirokawa N: Mechanism of the single-headed processivity: Diffusional anchoring between the K-loop of kinesin and the C terminus of tubulin. Proc Natl Acad Sci U S A 2000,97(2):640–645. 10.1073/pnas.97.2.640PubMed CentralPubMedView ArticleGoogle Scholar
- Helenius J, Brouhard G, Kalaidzidis Y, Diez S, Howard J: The depolymerizing kinesin MCAK uses lattice diffusion to rapidly target microtubule ends. Nature 2006,441(7089):115–119. 10.1038/nature04736PubMedView ArticleGoogle Scholar
- Asbury CL, Fehr AN, Block SM: Kinesin moves by an asymmetric hand-over-hand mechanism. Science 2003,302(5653):2130–2134. 10.1126/science.1092985PubMed CentralPubMedView ArticleGoogle Scholar
- Kaseda K, Higuchi H, Hirose K: Alternate fast and slow stepping of a heterodimeric kinesin molecule. Nat Cell Biol 2003,5(12):1079–1082. 10.1038/ncb1067PubMedView ArticleGoogle Scholar
- Yildiz A, Tomishige M, Vale RD, Selvin PR: Kinesin walks hand-over-hand. Science 2004,303(5658):676–678. 10.1126/science.1093753PubMedView ArticleGoogle Scholar
- Chakravarty A, Howard L, Compton DA: A Mechanistic Model for the Organization of Microtubule Asters by Motor and Non-Motor Proteins in a Mammalian Mitotic Extract. Mol Biol Cell 2004,15(5):2116–2132. 10.1091/mbc.E03-08-0579PubMed CentralPubMedView ArticleGoogle Scholar
- Cytrynbaum EN, Scholey JM, Mogilner A: A force balance model of early spindle pole separation in Drosophila embryos. Biophys J 2003,84(2):757–769.PubMed CentralPubMedView ArticleGoogle Scholar
- Gaglio T, Saredi A, Bingham JB, Hasbani MJ, Gill SR, Schroer TA, Compton DA: Opposing motor activities are required for the organization of the mammalian mitotic spindle pole. J Cell Biol 1996,135(2):399–414. 10.1083/jcb.135.2.399PubMedView ArticleGoogle Scholar
- Rosenfeld SS, Fordyce PM, Jefferson GM, King PH, Block SM: Stepping and stretching - How kinesin uses internal strain to walk processively. J Biol Chem 2003,278(20):18550–18556. 10.1074/jbc.M300849200PubMed CentralPubMedView ArticleGoogle Scholar
- Guydosh NR, Block SM: Backsteps induced by nucleotide analogs suggest the front head of kinesin is gated by strain. Proc Natl Acad Sci U S A 2006,103(21):8054–8059. 10.1073/pnas.0600931103PubMed CentralPubMedView ArticleGoogle Scholar
- Hancock WO, Howard J: Kinesin's processivity results from mechanical and chemical coordination between the ATP hydrolysis cycles of the two motor domains. Proc Natl Acad Sci U S A 1999,96(23):13147–13152. 10.1073/pnas.96.23.13147PubMed CentralPubMedView ArticleGoogle Scholar
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