Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.4.4 (kinesin)
 5,033 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An in vitro motility assay has been developed in which single actin filaments move on one or a few heavy meromyosin (HMM) molecules. This movement is slower than when many HMM molecules are involved, in contrast to analogous experiments with microtubules and kinesin. Frequency analysis shows that sliding speeds distribute around integral multiples of a unitary velocity. This discreteness may be due to differences in the numbers of HMM molecules interacting with each actin filament, where the unitary velocity reflects the activity of one HMM molecule. The value of the unitary velocity predicts a step size of 5-20 nm per ATP, which is consistent with the conventional swinging crossbridge model for myosin function.
 ...
PMID:Quantized velocities at low myosin densities in an in vitro motility assay. 185

The microtubule motor protein kinesin has been conjugated with 5-iodoacetamido fluorescein (5-IAF). The analogue, AF-kinesin, supports organelle motility and the movement of microtubules.
 ...
PMID:Studies using a fluorescent analogue of kinesin. 188 52

The nod (no distributive disjunction) and the ncd (non-claret disjunctional) mutations are both female-specific, recessive meiotic mutations in Drosophila melanogaster. Mutations at either locus show high frequencies of nondisjunction at meiosis I and both have been shown to encode kinesin-like proteins. Unlike the ncd mutation, which affects all chromosome pairs, the nod mutation affects only the disjunction of nonexchange chromosomes. Although both the nod and ncd mutations are fully recessive, females doubly heterozygous for nod and ncd mutations show levels of X and fourth chromosome nondisjunction that are 6- to 35-fold above those observed in control females. Exchange between chromosomes can suppress this effect; thus, only nonexchange chromosomes segregating via the distributive system are sensitive in double heterozygotes. Since the phenotype of double heterozygotes mimics that of the nod mutation, we infer that ncd is a dominant enhancer of nod. Failure of ncd to fully complement nod reveals the chromosome segregation machinery to be dosage sensitive. The probability that the distributive system will fail is enhanced in females simultaneously haploinsufficient at the nod and ncd loci.
 ...
PMID:Genetic analysis of microtubule motor proteins in Drosophila: a mutation at the ncd locus is a dominant enhancer of nod. 190 90

We have established an in vitro assay to characterize the binding of endocytic carrier vesicles to microtubules. Magnetic beads coated with microtubules were used as an affinity matrix. A fraction from nocodazole-treated cells enriched in endocytic carrier vesicles, labeled with internalized horseradish peroxidase, was used in the binding experiments. Binding of the endocytic carrier vesicles to microtubules in vitro was cytosol-dependent. This activity of cytosolic factors was saturable, heat-sensitive, and insensitive to N-ethyl-maleimide. Binding was sensitive to GTP and ATP. Addition of neuronal microtubule-associated proteins completely abolished binding of the endocytic organelles to microtubules. This binding was independent of the cytosolic microtubule-based motor proteins kinesin and cytoplasmic dynein, since cytosol depleted of these proteins remained fully active. Microtubule-binding proteins from HeLa cells, however, stimulated the interaction of endocytic carrier vesicles with microtubules. Trypsinized vesicles could no longer bind to microtubules in the presence of cytosol. These results suggest that cytosolic microtubule-binding proteins, other than the known microtubule-based motor proteins, as well as membrane proteins are involved in the nucleotide-dependent interaction of endocytic carrier vesicles with microtubules.
 ...
PMID:Motor protein independent binding of endocytic carrier vesicles to microtubules in vitro. 191 48

Recent evidence has suggested that the principal polypeptide component of the microtubule motor protein kinesin may be a member of an extended superfamily of related motor proteins. To gain insight into how large the kinesin superfamily might be and to begin determining the potential functions in which various superfamily members might participate, we identified and partially characterized six additional members of the Drosophila kinesin superfamily. Genes encoding these proteins were identified by using the polymerase chain reaction with degenerate primers corresponding to highly conserved regions of the kinesin heavy-chain motor domain. Partial sequencing of the six genes revealed that they encode proteins that are 40-60% identical to the motor domain of the kinesin heavy-chain sequence. The cytogenetic locations as well as the developmental and tissue-specific expression patterns have been determined. The data suggest that each of these six kinesin-like proteins may have functions in a wide variety of cell types and tissues.
 ...
PMID:Identification and partial characterization of six members of the kinesin superfamily in Drosophila. 192 6

Microtubules are the key elements of the cytoskeleton responsible for cytoplasm organization and intracellular transport. Their functions are realized mainly via microtubule associated proteins (MAP), the minor components bound to the microtubule core. Among MAP there are so-called structural proteins which control tubulin polymerization and provide the "static" interaction of microtubules with other intracellular components and translocator proteins. The latter are capable of moving the material along microtubules; this process is coupled with ATP hydrolysis. The first section summarizes the data on the composition and changes during ontogenesis and functioning, such as influences on tubulin polymerization and promotion of interactions between individual microtubules, between microtubules and microfilaments and neurofilaments as well as between microtubules and membrane organelles (lysosomes, golgi stacks, mitochondria). The second section deals with the description of translocators. The biochemical properties of the following proteins are considered: i) kinesin, the protein translocating particles to the distal end of microtubules and, ii) dynein which promotes translocation in the opposite direction.
 ...
PMID:[Microtubule-associated proteins]. 193 44

The underlying stochastic nature of many models of the actomyosin interaction should result in fluctuations in both force and shortening velocity. In classical experimental approaches involving intact or glycerinated muscle preparations these fluctuations are too small to resolve owing to the large numbers of crossbridges involved. However, new experimental techniques allow mechanical measurements to be made in systems in which small numbers of myosin heads act on a single actin filament, or small numbers of kinesin molecules act on a single tubulin filament. In these systems, stochastic effects should be evident. To understand better the nature of the expected stochastic effects, we have used computer simulation to investigate the fluctuations predicted by the original model for muscle crossbridge mechanics proposed by A.F. Huxley. We consider three situations: (1) the translation of actin or tubulin filaments by myosin or kinesin motors immobilized on a fixed substrate, (2) the production of tension by ensembles of immobilized myosin which involve the displacement of an elastic load, and (3) the fluctuations in axial displacement of a single, bipolar myosin thick filament interacting with actin filaments as in a sarcomere. In all three cases, fluctuations are clearly evident in simulations involving small numbers of motors. For case (1), we show that translation velocities can vary with crossbridge density. Whether one motor translates a filament faster, slower or at the same speed as many motors depends on the relative magnitudes of the attachment and detachment rate functions. Analytical expressions are provided to quantitate this relationship. For case (2), we show that fluctuations predicted assuming perfectly isometric conditions differ form those observed when the 'isometric state' is achieved against an elastic load. 'Elastic damping' of the fluctuations in the system results from the presence of many attached motors. In case (3) we show that in spite of the presence of stochastic fluctuations which can destabilize the uniformity of filament overlap in a sarcomere, the magnitude of thick filament displacement is less than might be anticipated over time periods of in vivo contraction. Taken together, these simulations allow one to better interpret experimental data in terms of current models of motor function.
 ...
PMID:Simulation of stochastic processes in motile crossbridge systems. 193 3

Movement of membrane-bounded organelles to intracellular destinations requires properly oriented microtubules and force-generating enzymes, such as the microtubule-stimulated ATPase kinesin. Kinesin is a heterotetramer with two heavy chain (approximately 124-kDa) and two light chain (approximately 64-kDa) subunits. Kinesin heavy chains contain both ATP- and microtubule-binding domains and are capable of force generation in vitro. Functions of the light chains are undetermined, although evidence suggests they interact with membrane surfaces. We have used molecular genetic approaches to dissect the kinesin light chain structure. Three distinct kinesin light chain cDNAs were cloned and sequenced from rat brain, and they were found to result from alternative splicing of a single gene. Polypeptides encoded by these cDNAs are identical except for their carboxyl ends. Synthesis of multiple light chains, differing from one another in primary structure, could provide a means of generating multiple, functionally specialized forms of the kinesin holoenzyme.
 ...
PMID:Molecular genetics of kinesin light chains: generation of isoforms by alternative splicing. 194 31

A protein of Mr 170,000 (170K protein) has been identified in HeLa cells, using an antiserum raised against HeLa nucleotide-sensitive microtubule-binding proteins. Affinity-purified antibodies specific for this 170K polypeptide were used for its characterization. In vitro sedimentation of the 170K protein with taxol microtubules polymerized from HeLa high-speed supernatant is enhanced in the presence of an ATP depleting system, but unaffected by the non-hydrolyzable ATP analogue AMP-PNP. In addition, it can be eluted from taxol microtubules by ATP or GTP, as well as NaCl. Thus it shows microtubule-binding characteristics distinct from those of the previously described classes of nucleotide-sensitive microtubule-binding proteins, the motor proteins kinesin and cytoplasmic dynein, homologues of which are also present in HeLa cells. The 170K protein sediments on sucrose gradients at approximately 6S, separate from kinesin (9.5S) and cytoplasmic dynein (20S), further indicating that it is not associated with these motor proteins. Immunofluorescence localization of the 170K protein shows a patchy distribution in interphase HeLa cells, often organized into linear arrays that correlate with microtubules. However, not all microtubules are labeled, and there is a significant accumulation of antigen at the peripheral ends of microtubules. In mitotic cells, 170K labeling is found in the spindle, but there is also dotty labeling in the cytoplasm. After depolymerization of microtubules by nocodazole, the staining pattern is also patchy but not organized in linear arrays, suggesting that the protein may be able to associate with other intracellular structures as well as microtubules. In vinblastine-treated cells, there is strong labeling of tubulin paracrystals, and random microtubules induced in vivo by taxol are also labeled by the antibodies. These immunofluorescence labeling patterns are stable to extraction of cells with Triton X-100 before fixation, further suggesting an association of the protein with cytoplasmic structures. In vivo, therefore, the 170K protein appears to be associated with a subset of microtubules at discrete sites. Its in vitro behavior suggests that it belongs to a novel class of nucleotide-sensitive microtubule-binding proteins.
 ...
PMID:Identification of a novel nucleotide-sensitive microtubule-binding protein in HeLa cells. 197 Aug 24

In the preceding paper we described pathways of mitotic spindle assembly in cell-free extracts prepared from eggs of Xenopus laevis. Here we demonstrate the poleward flux of microtubules in spindles assembled in vitro, using a photoactivatable fluorescein covalently coupled to tubulin and multi-channel fluorescence videomicroscopy. After local photoactivation of fluorescence by UV microbeam, we observed poleward movement of fluorescein-marked microtubules at a rate of 3 microns/min, similar to rates of chromosome movement and spindle elongation during prometaphase and anaphase. This movement could be blocked by the addition of millimolar AMP-PNP but was not affected by concentrations of vanadate up to 150 microM, suggesting that poleward flux may be driven by a microtubule motor similar to kinesin. In contrast to previous results obtained in vivo (Mitchison, T. J. 1989. J. Cell Biol. 109:637-652), poleward flux in vitro appears to occur independently of kinetochores or kinetochore microtubules, and therefore may be a general property of relatively stable microtubules within the spindle. We find that microtubules moving towards poles are dynamic structures, and we have estimated the average half-life of fluxing microtubules in vitro to be between approximately 75 and 100 s. We discuss these results with regard to the function of poleward flux in spindle movements in anaphase and prometaphase.
 ...
PMID:Poleward microtubule flux mitotic spindles assembled in vitro. 199 64


<< Previous 1 2 3 4 5 6 7 8 9 10