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)

We have investigated the kinetic properties of the slow plus end directed microtubule (MT) motor Eg5. The recombinantly expressed fusion protein E437GST, containing residues 12-437 of Eg5 fused to the N-terminus of glutathione S-transferase (GST), is dimeric and motile, translocating MTs at an average speed of 0.063 (+/-0.01) micrometers(-1). The kinetics of ATP turnover by E437GST were investigated using the fluorescent ATP analogue methylanthraniloyl-ATP (mantATP). In the absence of MTs, mantADP release from E437GST is slow (0.006 s(-1) in 50 mM NaCl) and rate-limiting. MTs accelerate this kinetic step approximately 850-fold to a maximal rate of 4.94 s(-1). Under these conditions, the steady-state rate of mantATP turnover was 1.92 s(-1), indicating that MT-activated mantADP release accounts for at least 40% of the total cycle time of the motor and is probably rate-limiting. This step is around 10-fold slower in Eg5 than in kinesin, consistent with it limiting the rate of physical stepping in both Eg5 and kinesin. The dissociation constants of the motor in the presence of various nucleotides were determined using MT pelleting assays. ADP stabilizes the weakest bound state of the motor, while ATP, ATP gamma S, AMPPNP, and apyrase all induce a shift toward tighter binding states. Overall, the data indicate that Eg5 displays strong kinetic homologies with the two other well-characterized MT motors, kinesin and non claret disjunctional, suggesting that all kinesin superfamily motors may share the same basic mechanochemistry.
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PMID:Kinetics and motility of the Eg5 microtubule motor. 865 78

A mechanism is proposed for molecular motors in which force is generated by a protein conformational change driven by binding energy (in muscle, that of myosin with actin as well as with ATP, ADP, or Pi). Work, the product of the force generated by one myosin or kinesin molecule (F) and the distance over which it acts (d), is a function of a ratio of dissociation constants before and after the contractile step: F.d < RT ln(KAe/KAc). From published data the ratio is > 2 x 10(4), which can be explained by conversion of a surface complex to an enclosed, or partly enclosed, complex. Although the complex performing the work stroke is in unstrained conformation, the complex after the work stroke is much more stable, owing to binding forces; the latter, however, is destabilized by the load, which thereby opposes the contractile conformational change, countering the force-generating reaction. The connection between the free energy release and work is implicit in the mechanism, inasmuch as coupling, like force generation, depends on conformational changes driven by binding energy (internal rather than external work being involved in coupling). The principles apply whether ATP or an ion gradient drives the system. At high load, in muscle, the mechanism allows for a summation of the forces generated by several myosin molecules.
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PMID:Force generation, work, and coupling in molecular motors. 878 46

The kinetic mechanism is analyzed for a monomeric human kinesin construct K332. In the absence of microtubules, the rate constants of the ATPase cycle are very similar to dimeric human kinesin K379 and whole kinesin from bovine brain. The microtubule-activated ATPase is 60 s(-1) at 20 degrees C; Km(Mt) is 5 microM; dissociation constants in the presence of ATP and ADP are 9 microM and 16 microM, respectively. The values of dissociation constants are 5 times larger than for K379. Binding of K332 to microtubules increased the rate of the hydrolysis step from 7 s(-1) to greater than 200 s(-1) and the 2'-(3')-O-(N-methylanthraniloyl) (mant) ADP dissociation step from 0.02 s(-1) to greater than 100 s(-1). At higher ionic strength, more than one ATP is hydrolyzed before dissociation of MtK332 (small processivity). Data are fitted to the kinetic scheme. [equation: see text] Approximate values of rate constants are k1 = 500 s(-1), k2 > or = 200 s(-1), k3k4/(k3 + k4) = 100 s(-1), k(dis) = 80+/-10 s(-1). Two experiments to measure k4 gave 110 s(-1) from the maximum rate of dissociation of mant ADP for reaction of K x ADP with microtubules and 300 s(-1) from extrapolation to zero concentration of rate of binding of mant ADP to MtK. It is proposed that mant ADP dissociation is a two-step process. In the simple scheme, k4 is the effective rate of the two-step release of ADP, k4 = 150 s(-1) to 200 s(-1), and k3 = 150 s(-1) to 200 s(-1) to account for the steady state rate.
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PMID:Kinetic mechanism of a monomeric kinesin construct. 899 55

Kinetic and equilibrium properties are compared for a monomeric kinesin construct (K332) and a dimeric construct (K379). MtK379 has a low affinity (5 x 10(4) M(-1)) and a high affinity (5 x 10(6) M(-1)) binding site for mant ADP while MtK332 has a single low affinity site (5 x 10(4) M(-1)). Rate constants of dissociation of mant ADP are <1 s(-1) for the high affinity site and 75-100 s(-1) for the low affinity site for MtK379. For MtK332, the effective rate constant is 200-300 s(-1). It is proposed that the two heads of the dimer are different through the interaction with the microtubule, a strongly bound head with low affinity for 2'-(3')-O-(N-methylanthraniloyl) adenosine 5'-diphosphate (mant ADP), similar to the single strongly bound head of the monomer and a weakly bound or detached head with high affinity for mant ADP. Rate of binding of mant ADP gave an "S"-shaped dependence on concentration for MtK379 and a hyperbolic dependence for MtK332. Binding of K379 x mant ADP dimer to microtubules releases only one mant ADP at a rate of 50 s(-1). The second strongly bound mant ADP is released by binding of nucleotides to the other head. Rates are 100 s(-1) for ATP, 30 s(-1) for AMPPNP or ATPgammaS, and 2 s(-1) for ADP. The rate of binding of mant ATP to MtK379 showed an "S"-shaped concentration dependence and limiting rate at zero concentration is <1 s(-1) while MtK332 gave a hyperbolic dependence and limiting rate of 100 s(-1). The limiting rate is determined by the rate of dissociation of mant ADP in the hydrolysis cycle. The evidence is consistent with an interacting site model in which binding of ATP to one head is required for release of ADP from the other head in the hydrolysis cycle. This model, in which the cycles are maintained partly out of phase, is an extension of the alternating site model of Hackney (Hackney, D. D. (1994) Proc. Nat. Acad. Sci. U.S.A. 91, 6865-6869). It provides a basis for a processive mechanism.
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PMID:Interacting head mechanism of microtubule-kinesin ATPase. 899 56

ncd is a microtubule motor protein from Drosophila, having a 40 kDa domain homologous to the kinesin motor domain. In the present study, we investigated the circular dichroism (CD) spectra of the ncd motor domain in comparison with those of the kinesin motor domain. Although the two are about 40% identical in amino acid sequence, and recent X-ray crystallographic studies [Sablin, Kull, Cooke, Vale, and Fletterick (1996) Nature 380, 555-559; Kull, Sablin, Lau, Fletterick, and Vale (1996) Nature 380, 550-555] indicate that their core structures are nearly identical, the far UV CD spectra of ncd and kinesin motor domains, both being monomeric, were considerably different from each other, suggesting a significant difference in the secondary, especially loop structures. The motor domain of ncd, like that of kinesin, contains tightly associating ADP even after purification. We removed ADP from the ncd motor domain by gel filtration in the presence of EDTA and high salt. The resultant protein, however, was likely to be in an inactive state, since it bound ATP slowly. The far UV CD spectrum of the ncd motor domain devoid of ADP was nearly identical to that of the ncd motor domain with bound ADP. This indicated that the removal of ADP did not affect the backbone structure in the presence of high salt. On the other hand, the near UV CD spectrum of the ADP-free ncd motor domain differed from that of the ncd motor domain. ADP complex, one possibility being that the local conformation was changed upon removal of bound ADP. The near UV CD spectra of kinesin motor domain also showed a difference between the ADP-bound form and the nucleotide-free form, although the difference was much smaller.
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PMID:Comparison of ncd and kinesin motor domains by circular dichroism spectroscopy. 901 Jul 67

Transient kinetic analysis of microtubule-stimulated ATP hydrolysis by the monomeric kinesin motor domain DKH357 was performed to investigate the kinetic pattern of a monomer. Both ATP and ADP produced dissociation of the complex, microtubule (MT).E, of microtubules with DKH357 at a maximum rate of approximately 45 s-1 as determined by decrease in turbidity. The maximum dissociation rate was independent of the KCl concentration between 25 and 200 mM. At subsaturating levels of nucleotide, ATP was more effective than ADP in dissociating DKH357 from MT.E (1.6 and 0.4 microM-1 s-1 for ATP and ADP, respectively, at 50 mM KCl). Addition of ATP to MT.E results in a burst of product formation with a maximum initial rate of approximately 100 s-1 at saturating levels of ATP. This maximum hydrolysis rate of 100 s-1 is similar to the maximum steady state ATPase rate at saturating microtubules of approximately 70 s-1, and thus hydrolysis is at least partially rate-limiting. When the MT lattice was highly occupied with bound DKH357, the amplitude of the burst was approximately 2 per DKH357 active site (superstoichiometric). The rate constant for the burst transient was approximately 45 s-1, which is the same as the rate for dissociation of DKH357 from the microtubule and this suggests that dissociation and termination of the burst phase are coupled. The size of the burst increased with decreasing initial occupancy of the MT lattice with bound DKH357 and approached the value of approximately 4 ATP molecules predicted by previous steady state measurements (Jiang, W., Stock, M., Li, X., and Hackney, D. D., submitted for publication).
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PMID:Monomeric kinesin head domains hydrolyze multiple ATP molecules before release from a microtubule. 903 70

The role of ATP hydrolysis by the 44/62 protein in formation of the stable holoenzyme DNA replication complex has been further elucidated by specifically examining the role that the 44/62 protein plays in loading the 45 protein onto the DNA substrate. A stable phospho-45 protein or phosphorylated holoenzyme complex was not detected or isolated, suggesting that the 44/62 protein may not act as a protein kinase. Product and dead-end inhibition data are consistent with an ordered kinetic mechanism with respect to product release in which phosphate is released from the 44/62 protein prior to ADP. Positional isotope effect studies support this mechanism and failed to demonstrate that ATP hydrolysis by the 44/62 protein is reversible. Steady-state ATPase assays using aluminum tetrafluoride as an inhibitor are also consistent with release of ADP being partially rate-limiting. Aluminum tetrafluoride acts to trap ADP on the enzyme after turnover, forming a stable transition state analog that dissociates slowly from the enzyme. Processive DNA synthesis does not occur using the accessory proteins in the presence of pre- or post-hydrolysis analogs of ATP nor in the presence of ADP-AlF4, indicating that turnover of the 44/62 protein is absolutely required for formation of the holoenzyme complex. Collectively, data obtained regarding ATP hydrolysis by the 44/62 protein are described in terms of the clamp loading protein functioning as a molecular motor, similar to other systems including myosin and kinesin.
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PMID:Mechanism of bacteriophage T4 DNA holoenzyme assembly: the 44/62 protein acts as a molecular motor. 906

Motor domains of kinesin were expressed that extend from the N terminus to positions 346, 357, 365, 381, and 405 (designated DKH346-DKH405) to determine if the kinetic differences observed between monomeric DKH340 and dimeric DKH392 (Hackney, D. D. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 6865-6869) were specific to these constructs or due to their oligomeric state. Sedimentation analysis indicated that DKH346, DKH357, and DKH365 are predominantly monomeric and that DKH381 and DKH405 are predominantly dimeric at 0. 01-0.03 microM, the concentrations used for ATPase assays. In buffer with 25 mM KCl, all have high kcat values of 38-96 s-1 at saturating microtubule (MT) levels. Monomeric DKH346, DKH357, and DKH365 have K0.5(MT) values of 17, 9, and 1.4 microM, respectively, but the K0. 5(MT) values for the dimeric species are significantly lower, with 0. 02 and 0.14 microM for DKH381 and DKH405, respectively. The three new monomers release all of their ADP on association with microtubules, whereas the two new dimers retain approximately half of their ADP, consistent with the half-site reactivity observed previously with dimeric DKH392. Both the kbi(ATPase) (=kcat/K0. 5(MT)) values for stimulation of ATPase by MTs and the kbi(ADP) for stimulation of ADP release by MTs were determined in buffer containing 120 mM potassium acetate. The ratio of these rate constants (kbi(ratio) = kbi(ATPase)/kbi(ADP)) is 60-100 for the dimers, indicating hydrolysis of many ATP molecules per productive encounter with a MT as observed previously for DKH392 (Hackney, D. D. (1995) Nature 377, 448-450). For the monomers, kbi(ratio) values of approximately 4 indicate that they also may hydrolyze more than one ATP molecule per encounter with a MT and that the mechanism of hydrolysis is therefore fundamentally different from that of actomyosin. DKH340 is an exception to this pattern and may undergo uncoupled ATP hydrolysis.
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PMID:Influence of the kinesin neck domain on dimerization and ATPase kinetics. 906 17

The structures of the oppositely directed microtubule motors kinesin and ncd have been solved to atomic resolution. The two structures are very similar and are also homologous to myosin. Myosins and kinesins differ kinetically but, tantalizingly, cryoelectron microscopy has recently revealed that both structures may tilt during ADP release. Such evidence suggests that the two motor families use common structural mechanisms.
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PMID:Structure and dynamics of molecular motors. 909 28

The Acanthamoeba myosin-IA and myosin-IB molecular motors bind to membranes, so they may produce the force to move organelles and membranes along actin filaments. We have determined the rate constants for the actin-activated myosin-I ATPase by pre-steady state kinetic analysis. ATP binds rapidly to myosin-I and dissociates the enzyme from actin filaments at a rate > 500 s-1. Myosin-I hydrolyzes ATP to ADP and inorganic phosphate (Pi) at 20-50 s-1. Phosphate dissociation is the rate limiting step in the ATPase cycle, 0.01 s-1 for myosin-I alone and at 10 s-1 when myosin-I is bound to actin filaments. ADP dissociation is rapid. Phosphorylation controls the ATPase cycle by increasing the rate of phosphate release from myosin-I bound to actin. At steady state the major species are myosin-ATP and myosin-ADP-Pi, which rapidly bind to and dissociate from actin filaments. During the ATPase cycle myosin-I binds so weakly to actin filaments that it cannot support processive movement like kinesin, unless several motors cluster together on a membrane or actin filament. These properties of the enzyme emphasize the importance of characterizing mechanisms that promote the self-association of myosin-I isoforms at specific binding sites in cells.
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PMID:The chemical mechanism of myosin-I: implications for actin-based motility and the evolution of the myosin family of motor proteins. 911 40


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