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First published online September 20, 2006
doi: 10.1242/10.1242/jcs.03224

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Lucky 13 - microtubule depolymerisation by kinesin-13 motors

¹ School of Crystallography, Birkbeck College, Malet Street, London, WC1E 7HX, UK
² Department of Cell Biology, CB227, The Scripps Research Institute, 10550 N. Torrey Pines Road, La Jolla, CA 92037, USA

View larger version (14K): [in a new window]   Fig. 1. MT dynamic instability. (Left to right) GTP-tubulin (dark green) adopts a straight conformation that favours MT polymerisation. MT polymers are polar with ß-tubulin at the plus end and -tubulin at the minus end. Dynamic instability occurs at both ends but only the plus end is illustrated for clarity. GTP is hydrolysed within the MT lattice to GDP (light green) but GDP-tubulin is held in place by the lattice until hydrolysis occurs at the MT end, catastrophe occurs and MTs depolymerise.

View larger version (68K): [in a new window]   Fig. 2. Kinesin-13 molecular architecture. (A) Kinesin-13 domain organisation. The same colour scheme of the neck+motor region is used throughout the figures. (B) Sequence alignment of neck+motor constructs of select kinesin-13 motors with the motor core from human kinesin-1. The nucleotide-binding motifs, N1-N4, are as described by Sablin et al. (Sablin et al., 1996). The alignment was performed using T-Coffee (Notredame et al., 2000) and visualised using ESPript (http://espript.ibcp.fr/ESPript/ESPript/index.php). Sequences used: Homo sapiens kinesin-1, X65873; Homo sapiens MCAK, Q99661; Homo sapiens KIF2A, O00139; Drosophila melanogaster KLP59C, AE003459; Drosophila melanogaster KLP10A, AE003485; Plasmodium falciparum PFL2165w, AE014851.

View larger version (50K): [in a new window]   Fig. 3. Kinesin-13 motor domain structure. (A) 3D ribbon structure of the Plasmodium falciparum kinesin-13 motor core (Shipley et al., 2004). Orthogonal views are shown in which the `front' view is as if the MT surface were behind the motor domain; the top of the motor domain would point towards the MT plus end. The -helices are shown in dark blue and are individually labelled and the ß-sheets are shown in light blue. The pdb code for this structure is 1RY6. (B) Schematic of the interaction between the MT lattice and a kinesin motor domain. (C) 3D ribbon structure of the Homo sapiens MCAK neck+motor construct (Ogawa et al., 2004). The visible portion of the neck region is shown in orange but only represents about a third of the total neck sequence (see alignment in Fig. 2B). The left-hand view shows the front of the motor and the right-hand view shows a 90° rotation, as if viewing the motor-MT interaction from the side. The green line indicates where the MT surface would be and shows that the curvature of the motor domain would match the more curved surface of flexible tubulin dimers at MT ends. The pdb code for this structure is 1V8K. Atomic structures were displayed using PyMOL (http://www.pymol.org).

View larger version (33K): [in a new window]   Fig. 4. The kinesin-13 ATPase cycle. Kinesin-13 motors use ATP to depolymerise MTs and their ATPase cycle is controlled by whether depolymerisation can (at MT ends) or cannot (on the MT lattice) occur. The MT end is thought to have distinct structural and/or conformational properties that allow it to be recognised by kinesin-13 motors and +TIPs. (It is these distinct properties that are believed to be shared, to some extent, by individual tubulin heterodimers and explains why the ATPase activity of kinesin-13 motors can be stimulated by them.) In the diagram, terminal tubulins are depicted with dotted outlines. On the left side, the behaviour of a kinesin-13 motor core is illustrated. The nucleotide state of this motor core in solution is not known but when it binds the MT lattice, ADP is released; a conformational change that presumably corresponds to this release step is observed in cryo-EM maps (Moores et al., 2003). However, the ATPase activity of the motor is inhibited by the lattice and no further conformational changes are seen, which supports the idea that the ATPase cycle of the motor is blocked on the lattice prior to ATP binding (Moores et al., 2003). At the MT end, however, the motor ATPase activity is stimulated, which suggests that ATP can bind. The ATP binding step (mimicked by AMPPNP) is the only point at which bent tubulin intermediates, representing the active deformation of the terminal tubulins by the kinesin motor, are observed (Moores et al., 2002). By contrast, dimeric kinesin-13 (on the right) in solution contains ADP.Pi and undergoes 1D diffusion along the lattice in this nucleotide state; ATP is not required for this process (Helenius et al., 2006). Once at the MT end, because ATP is required for depolymerisation, presumably ADP and Pi must be lost from at least one motor domain before ATP can bind and depolymerisation can occur. Presumably, there is a similar coupling between ATP binding by the dimer and bending of the terminal tubulin (Desai et al., 1999).

View larger version (46K): [in a new window]   Fig. 5. Roles of kinesin-13 motors during mitosis. (A) Schematic of the stages of mitosis when kinesin-13 motors are known to be active. Chromosomes are shown in blue with a black kinetochore, spindle MTs are in green, centriole pairs are in dark green and the location of active kinesin-13 motors is indicated by red asterisks. (B) Localisation of KLP10A (mainly at the spindle poles) and KLP59C (mainly at the kinetochore) during cell division in Drosophila S2 tissue culture cells. Bar, 5 mm. Reprinted from Rogers et al. (Rogers et al., 2004) with permission from Macmillan Publishers Ltd.