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)

Our detailed measurements of the movements of kinesin- and dynein-coated latex beads have revealed several important features of the motors which underlie basic mechanical aspects of the mechanisms of motor movements. Kinesin-coated beads will move along the paths of individual microtubule protofilaments with high fidelity and will pause at 4 nm intervals along the microtubule axis under low ATP conditions. In contrast, cytoplasmic dynein-coated beads move laterally across many protofilaments as they travel along the microtubule, without any regular pauses, suggesting that the movements of kinesin-coated beads are not an artefact of the method. These kinesin bead movements suggest a model for kinesin movement in which the two heads walk along an individual protofilament in a hand-over-hand fashion. A free head would only be able to bind to the next forward tubulin subunit on the protofilament and its binding would pull off the trailing head to start the cycle again. This model is consistent with the observed cooperativity between the heads and with the movement by single dimeric molecules. Several testable predictions of the model are that kinesin should be able to bind to both alpha and beta tubulin and that the length of the neck region of the molecule should control the off-axis motility. In this article, we describe the technology for measuring nanometer-level movements and the force generated by the kinesin molecule.
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PMID:A model for kinesin movement from nanometer-level movements of kinesin and cytoplasmic dynein and force measurements. 183 66

Apolipoprotein E (apoE) is involved in the development and regeneration of the central nervous system (CNS). ApoE may also be necessary to maintain the integrity of the synapto-dendritic complexity. We analyzed the synaptic alterations in the CNS of apoE-deficient (knockout) mice during the aging process. In apoE-deficient homozygous mice, there was an age-dependent 15 to 40% loss of synaptophysin-immunoreactive nerve terminals and microtubule-associated protein 2-immunoreactive dendrites in the neocortex and hippocampus, when compared to controls. Dendritic alterations were observed as early as 4 months of age. Ultrastructural analysis revealed extensive dendritic vacuolization and disruption of the endomembrane system and cytoskeleton in apoE-deficient homozygous mice. Further immunocytochemical studies of the neuronal cytoskeleton showed that in apoE-deficient mice there was a decrease in the immunoreactivity of alpha and beta tubulin (but not kinesin) in the cell bodies and processes. These results support the contention that apoE might play an important role in maintaining the stability of the synapto-dendritic apparatus and that altered or deficient functioning of this molecule could underlie the synaptic and cytoskeletal alterations in Alzheimer's disease.
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PMID:Neurodegeneration in the central nervous system of apoE-deficient mice. 749 1

The kinesin superfamily is a class of microtubule-based mechano-enzymes involved in intracellular transport and chromosome movements. Molecules that move towards either the plus end or the minus end of microtubules are represented within the family. The motor domains of these molecules exhibit considerable sequence homology and contain both the ATP- and microtubule-binding sites (reviewed in refs 1, 2). Here we focus on non-claret disjunctional (ncd), a minus-end-directed motor involved in chromosome segregation in meiosis and early mitosis in Drosophila. We have calculated a three-dimensional map of tubulin sheets decorated with monomeric recombinant ncd motor domains by negative-stain electron microscopy and image analysis. Comparisons with a control structure of tubulin alone reveal that each motor domain binds to the crest of a single protofilament, making extensive contacts with both the alpha and beta tubulin monomers. Binding of the motor domain results in significant conformational changes in both of the tubulin monomers.
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PMID:Three-dimensional structure of a tubulin-motor-protein complex. 761 26

Kinesin and ncd (non-claret disjunctional) are microtubule associated motor proteins which share several structural features: both motors are dimers; each monomer is composed of a stalk region, a cargo binding domain and a motor domain; the motor domains have approximately 41% sequence identity. Despite these similarities the two motors have strikingly different movement properties: kinesin is a plus-end directed molecular motor, while ncd is minus-end directed. Here we compare the structure and the microtubule-binding properties of these oppositely directed molecular motors. We determined the three-dimensional structure of tubulin sheets decorated with the motor domains of either kinesin or ncd to a resolution of < 20 A by negative stain electron microscopy and tilt series reconstruction. Comparisons with a control structure of tubulin alone revealed that in both cases the motor domain binds to the outer crest of a single protofilament making contacts with both alpha and beta tubulin. Despite their opposite directionality, the geometry of attachment of the motor domain to the protofilament in the presence of AMP-PNP is very similar for both motors. These data rule out models for directionality which have the motors binding in an opposite orientation to the microtubules. Binding of the ncd as well as the kinesin motor domain appears to induce conformational changes in tubulin. This observation suggests an active role of tubulin in motor movement and/or in the determination of directionality.
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PMID:Motor domains of kinesin and ncd interact with microtubule protofilaments with the same binding geometry. 904 48

Calponin is a basic smooth muscle protein capable of binding to actin, calmodulin, tropomyosin, and phospholipids. We have found that the basic calponin interacted with brain tubulin under polymerized and unpolymerized conditions in vitro [Fujii, T., Hiromori, T., Hamamoto, M., and Suzuki, T. (1997) J. Biochem. 122, 344-351]. We examined the calponin-binding site on the tubulin molecule by sedimentation, limited digestion, chemical-cross linking, immunoblotting, and delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometric (DE MALDI-TOF) analyses. Calponin interacts with both the alpha and beta tubulins and only slightly with the tyrosinated and acetylated form of alpha tubulin. The binding of calponin to microtubules was blocked by adding poly(L-aspartic acid) (PLAA) or MAP2. After digestion of microtubule proteins with subtilisin, the amount of calponin binding to alphabetas microtubules was reduced compared to native microtubules, but no further reduction was observed in the case of alphasbetas microtubules. The chemical cross-linked products of calponin and synthesized peptides (KDYEEVGVDSVEGE; alpha-KE) derived from the C-terminal region of alpha tubulin and (YQQYQDATADEQG; beta-YG) and (GEFEEEGEEDEA; beta-GA) from that of beta tubulin were detected by mass spectrometry. One kind of calponin-peptide complex was formed in the presence of alpha-KE or beta-YG, while five complexes (calponin:peptide = 1:1-5) were generated in the presence of beta-GA. Peptides alpha-KE and beta-GA inhibited the binding of calponin to tubulin produced by EDC in a concentration-dependent manner. These findings suggest that basic calponin interacts with both tubulin subunits and that their C-terminal regions, which also contain the binding sites of MAP2, tau, and kinesin, may be involved in calponin-binding.
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PMID:Identification of the binding region of basic calponin on alpha and beta tubulins. 1022 May 77

Ncd is a microtubule minus-end directed motor of the kinesin superfamily. Previously it has been shown that ncd and kinesin motor domains share the same major binding site on microtubules. Here we report a three-dimensional EM reconstruction of negatively stained two-dimensional Zn-induced tubulin crystal sheets (Zn-sheets) decorated with the ncd motor domain at a resolution of 16 A. This work has revealed a second specific binding site for the ncd motor domain. The motor binding site on the tubulin Zn-sheets spans both alpha and beta tubulin subunits. This binding site is located at a position different from the previously identified ncd binding site on microtubules and may play a role in motor function.
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PMID:Visualizing a new binding site of ncd-motor domain on tubulin. 1060 May 55

In microtubule (MT) translocation assays, using colloidal gold particles coupled to monoclonal tubulin antibodies to mark positions along MTs, we found that relative motion is possible between the gold particle and an MT, gliding on dynein or kinesin. Such motion evidently occurred by an affinity release and rebinding mechanism that did not require motor activity on the particle. As the MTs moved, particles drifted to the trailing edge of the MT and then were released. Sometimes the particles transferred from one MT to another, moving orthogonally. Although motion of the particles was uniformly rearward, movement was toward the (-) or (+) end of the MT, depending on whether dynein or kinesin, respectively, was used in the assay. These results open possibilities for physiological mechanisms of organelle and other movement that, although dependent on motor-driven microtubule transport, do not require direct motor attachment between the organelle and the microtubule. Our observations on the direction of particle drift and time of release may also provide confirmation in a dynamic system for the conclusion that beta tubulin is exposed at the (+) end of the MT.
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PMID:Evidence for a novel affinity mechanism of motor-assisted transport along microtubules. 1063 99

Kinesins are a family of microtubule-dependent motor proteins that carry cargoes such as vesicles, organelles, or protein complexes along microtubules. Here we summarize structural studies of the "conventional" motor protein kinesin-1 and its interactions with microtubules, as determined by X-ray crystallography and cryo-electron microscopy. In particular, we consider the docking between the kinesin motor domain and tubulin subunits and summarize the evidence that kinesin binds mainly to beta tubulin with the switch-2 helix close to the intradimer interface between alpha and beta tubulin.
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PMID:Interaction of kinesin motors, microtubules, and MAPs. 1636 23