Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.4.4 (kinesin)
5,033 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The microtubule cytoskeleton is a dynamic structure in which the lengths of the microtubules are tightly regulated. One regulatory mechanism is the depolymerization of microtubules by motor proteins in the kinesin-13 family. These proteins are crucial for the control of microtubule length in cell division, neuronal development and interphase microtubule dynamics. The mechanism by which kinesin-13 proteins depolymerize microtubules is poorly understood. A central question is how these proteins target to microtubule ends at rates exceeding those of standard enzyme-substrate kinetics. To address this question we developed a single-molecule microscopy assay for MCAK, the founding member of the kinesin-13 family. Here we show that MCAK moves along the microtubule lattice in a one-dimensional (1D) random walk. MCAK-microtubule interactions were transient: the average MCAK molecule diffused for 0.83 s with a diffusion coefficient of 0.38 microm2 s(-1). Although the catalytic depolymerization by MCAK requires the hydrolysis of ATP, we found that the diffusion did not. The transient transition from three-dimensional diffusion to 1D diffusion corresponds to a "reduction in dimensionality" that has been proposed as the search strategy by which DNA enzymes find specific binding sites. We show that MCAK uses this strategy to target to both microtubule ends more rapidly than direct binding from solution.
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PMID:The depolymerizing kinesin MCAK uses lattice diffusion to rapidly target microtubule ends. 1667 73

The microtubule cytoskeleton and the mitotic spindle are highly dynamic structures, yet their sizes are remarkably constant, thus indicating that the growth and shrinkage of their constituent microtubules are finely balanced. This balance is achieved, in part, through kinesin-8 proteins (such as Kip3p in budding yeast and KLP67A in Drosophila) that destabilize microtubules. Here, we directly demonstrate that Kip3p destabilizes microtubules by depolymerizing them--accounting for the effects of kinesin-8 perturbations on microtubule and spindle length observed in fungi and metazoan cells. Furthermore, using single-molecule microscopy assays, we show that Kip3p has several properties that distinguish it from other depolymerizing kinesins, such as the kinesin-13 MCAK. First, Kip3p disassembles microtubules exclusively at the plus end and second, remarkably, Kip3p depolymerizes longer microtubules faster than shorter ones. These properties are consequences of Kip3p being a highly processive, plus-end-directed motor, both in vitro and in vivo. Length-dependent depolymerization provides a new mechanism for controlling the lengths of subcellular structures.
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PMID:Yeast kinesin-8 depolymerizes microtubules in a length-dependent manner. 1694 36

To ensure genetic integrity, replicated chromosomes must be accurately distributed to daughter cells-a process that is accomplished on the microtubule spindle. Kinesin-13 motors play an essential role in this process by performing regulated microtubule depolymerization. We set out to dissect the depolymerization mechanism of these kinesins, and in particular, the role of their conserved neck sequence. We used a monomeric kinesin-13 MCAK, consisting of the neck and motor core, which has strong depolymerizing activity. In the presence of a non-hydrolysable ATP analogue, this construct induced formation of rings around microtubules. The rings are built from tubulin protofilaments that are bent by the kinesin-13 motor engaged at the ATP-binding step of its ATPase cycle. Our data suggest that the ring-microtubule interaction is mediated by the neck and support the idea of a role for the kinesin-13 neck in depolymerization efficiency, acting by optimizing release of tubulin from microtubule ends.
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PMID:The role of the kinesin-13 neck in microtubule depolymerization. 1692 84

The variety of shapes and sizes of the microtubule cytoskeleton is as great as the number of different cell types. This large variety is a consequence of the dynamic properties of microtubules, which allow them to adopt distributions of arbitrary size and form. How is the distribution of microtubule lengths controlled? Recent work suggests that the length distribution is controlled, at least in part, by the activity of microtubule polymerases and depolymerases, which accelerate microtubule growth and shrinkage. Specifically, biochemical and single-molecule studies have shown how MCAK (kinesin-13) and Kip3p (kinesin-8) accelerate depolymerization and how XMAP215 may accelerate growth. Studies on the yeast Dam1 complex have shown how proteins can couple a cellular structure, the kinetochore, to the ends of polymerizing and depolymerizing microtubules.
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PMID:Microtubule polymerases and depolymerases. 1718 86

Cilia and flagella are complex, microtubule (MT)-filled cell organelles of which the structure is evolutionarily conserved from protistan cells to mammalian sperm and the size is regulated. The best-established model for flagellar length (FL) control is set by the balance of continuous MT assembly and disassembly occurring at the flagellar tip. Because steady-state assembly of tubulin onto the distal end of the flagellum requires intraflagellar transport (IFT)--a bidirectional movement of large protein complexes that occurs within the flagellum--FL control must rely upon the regulation of IFT. This does not preclude that other pathways might "directly" affect MT assembly and disassembly. Now, among the superfamily of kinesins, family-13 (MCAK/KIF2) members exhibit a MT-depolymerizing activity responsible for their essential functions in mitosis. Here we present a novel family-13 kinesin from the flagellated protozoan parasite Leishmania major, that localizes essentially to the flagellum, and whose overexpression produces flagellar shortening and knockdown yields long flagella. Using negative mutants, we demonstrate that this phenotype is linked with the MT-binding and -depolymerizing activity of this kinesin. This is the first report of an effector protein involved in FL control through a direct action in MT dynamics, thus this finding complements the assembly-disassembly model.
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PMID:A novel microtubule-depolymerizing kinesin involved in length control of a eukaryotic flagellum. 1743 82

The human genome has three unique genes coding for kinesin-13 proteins called Kif2a, Kif2b, and MCAK (Kif2c). Kif2a and MCAK have documented roles in mitosis, but the function of Kif2b has not been defined. Here, we show that Kif2b is expressed at very low levels in cultured cells and that GFP-Kif2b localizes predominately to centrosomes and midbodies, but also to spindle microtubules and transiently to kinetochores. Kif2b-deficient cells assemble monopolar or disorganized spindles. Chromosomes in Kif2b-deficient cells show typical kinetochore-microtubule attachments, but the velocity of movement is reduced approximately 80% compared with control cells. Some Kif2b-deficient cells attempt anaphase, but the cleavage furrow regresses and cytokinesis fails. Like Kif2a-deficient cells, bipolar spindle assembly can be restored to Kif2b-deficient cells by simultaneous deficiency of MCAK or Nuf2 or treatment with low doses of nocodazole. However, Kif2b-deficient cells are unique in that they assemble bipolar spindles when the pole focusing activities of NuMA and HSET are perturbed. These data demonstrate that Kif2b function is required for spindle assembly and chromosome movement and that the microtubule depolymerase activities of Kif2a, Kif2b, and MCAK fulfill distinct functions during mitosis in human cells.
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PMID:The kinesin-13 proteins Kif2a, Kif2b, and Kif2c/MCAK have distinct roles during mitosis in human cells. 1753 14

The microtubule (MT)-associated protein EB1 localizes to and promotes growth at MT plus ends. The MT depolymerizing kinesin MCAK has also been reported to track growing MT plus ends. Here, we confirm that human MCAK colocalizes with EB1 at growing MT ends when expressed as a GFP fusion protein in transfected cells. We show that MCAK associates with the C-terminus of EB1 and EB3 but much less efficiently with RP1. EB1 associates with the N-terminal localization and regulatory domain in MCAK but not with the motor domain of the protein. The interaction is competitive with the binding of other EB1 ligands and does not require MTs. Knockdown of EB1 expression using siRNA impaired the ability of GFP-MCAK to localize to MT tips in transfected cells. We propose that MCAK is targeted to growing MT ends by EB1, that MCAK is held in an inactive conformation when associated with EB1 and that this could provide the basis for a mechanism that facilitates rapid switching between phases of MT growth and depolymerization.
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PMID:MCAK associates with EB1. 1796 21

Dynamic microtubules are necessary for proper mitotic spindle assembly and chromosome segregation during mitosis. Members of the kinesin superfamily of molecular motor proteins are important to spindle function. Of particular interest is the Kinesin-13 family member MCAK, which acts to regulate microtubule dynamics during spindle assembly and to ensure proper attachments of chromosomes to spindle microtubules. The unique ability of MCAK to regulate microtubule dynamics makes it a potential target for development of new drugs that alter spindle function. Here, we knocked down MCAK via RNAi in normal and malignant cell lines and found that the two tested malignant cell lines were acutely sensitive to MCAK knockdown, while the tested normal cells were less sensitive. In addition, we looked at the effect of combining MCAK knockdown and drug treatment with paclitaxel or vinblastine to identify spindle assembly defects. We found that MCAK knockdown increased the morphological defects of the microtubule cytoskeleton in HeLa cells caused by anti-microtubule drugs. Our studies support the idea that MCAK would be a good target for new chemotherapeutic development and may be particularly useful in combination therapies with currently available anti-microtubule agents.
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PMID:Effects of anti-microtubule agents on microtubule organization in cells lacking the kinesin-13 MCAK. 1863 58

The formation of a functional bipolar mitotic spindle is essential for genetic integrity. In human cells, the microtubule polymerase XMAP215/ch-Tog ensures spindle bipolarity by counteracting the activity of the microtubule-depolymerizing kinesin XKCM1/MCAK. Their antagonistic effects on microtubule polymerization confer dynamic instability on microtubules assembled in cell-free systems. It is, however, unclear if a similar interplay governs microtubule behavior in mammalian cells in vivo. Using real-time analysis of spindle assembly, we found that ch-Tog is required to produce or maintain long centrosomal microtubules after nuclear-envelope breakdown. In the absence of ch-Tog, microtubule assembly at centrosomes was impaired and microtubules were nondynamic. Interkinetochore distances and the lengths of kinetochore fibers were also reduced in these cells. Codepleting MCAK with ch-Tog improved kinetochore fiber length and interkinetochore separation but, surprisingly, did not rescue centrosomal microtubule assembly and microtubule dynamics. Our data therefore suggest that ch-Tog has at least two distinct roles in spindle formation. First, it protects kinetochore microtubules from depolymerization by MCAK. Second, ch-Tog plays an essential role in centrosomal microtubule assembly, a function independent of MCAK activity. Thus, the notion that the antagonistic activities of MCAK and ch-Tog determine overall microtubule stability is too simplistic to apply to human cells.
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PMID:MCAK-independent functions of ch-Tog/XMAP215 in microtubule plus-end dynamics. 1880 77

MCAK, a kinesin related motor protein with microtubule depolymerizing activity, is known to play an important role in spindle assembly and correcting errors in mitotic chromosome alignment. Experiments to determine how cellular levels of the protein are regulated demonstrate that MCAK accumulates during cell cycle progression, reaches a maximum at G(2)/M phase, and is rapidly degraded by the proteasome during mitosis. Immunofluorescence microscopy further indicates that MCAK largely disappears from kinetochores and spindle poles at the metaphase to anaphase transition. A phosphorylated form of MCAK appears during mitosis and seems to be preferentially degraded, but degradation does not appear to depend on Aurora B, a kinase reported to be involved in regulating the error correcting activity of the protein. These studies indicate that MCAK activity is limited during the latter stages of mitosis by protein degradation, and argue against a role for the protein in anaphase chromosome movement.
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PMID:Cell cycle dependent degradation of MCAK: evidence against a role in anaphase chromosome movement. 1884


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