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 quaternary structures of several monomeric and dimeric kinesin constructs from Homo sapiens and Drosophila melanogaster were analyzed using small angle x-ray and neutron scattering. The experimental scattering curves of these proteins were compared with simulated scattering curves calculated from available crystallographic coordinates. These comparisons indicate that the overall conformations of the solution structures of D. melanogaster and H. sapiens kinesin heavy chain dimers are compatible with the crystal structure of dimeric kinesin from Rattus norvegicus. This suggests that the unusual asymmetric conformation of dimeric kinesin in the microtubule-independent ADP state is likely to be a general feature of the kinesin heavy chain subfamily. An intermediate length Drosophila construct (365 residues) is mostly monomeric at low protein concentration whereas at higher concentrations it is dimeric with a tendency to form higher oligomers.
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PMID:The overall conformation of conventional kinesins studied by small angle X-ray and neutron scattering. 1102 Mar 87

Success of mitosis depends upon the coordinated and regulated activity of many cellular factors, including kinesin motor proteins, which are required for the assembly and function of the mitotic spindle. Eg5 is a kinesin implicated in the formation of the bipolar spindle and its movement prior to and during anaphase. We have determined the crystal structure of the Eg5 motor domain with ADP-Mg bound. This structure revealed a new intramolecular binding site of the neck-linker. In other kinesins, the neck-linker has been shown to be a critical mechanical element for force generation. The neck-linker of conventional kinesin is believed to undergo an ordered-to-disordered transition as it translocates along a microtubule. The structure of Eg5 showed an ordered neck-linker conformation in a position never observed previously. The docking of the neck-linker relies upon residues conserved only in the Eg5 subfamily of kinesin motors. Based on this new information, we suggest that the neck-linker of Eg5 may undergo an ordered-to-ordered transition during force production. This ratchet-like mechanism is consistent with the biological activity of Eg5.
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PMID:Crystal structure of the mitotic spindle kinesin Eg5 reveals a novel conformation of the neck-linker. 1132 9

Kinesin is an ATP-driven molecular motor protein that moves processively along microtubules. Despite considerable research, the detailed mechanism of kinesin motion remains elusive. We applied an enhanced suite of single- and multiple-molecule fluorescence polarization microscopy assays to report the orientation and mobility of kinesin molecules bound to microtubules as a function of nucleotide state. In the presence of analogs of ATP, ADP-Pi or in the absence of nucleotide, the kinesin head maintains a rigid orientation. In the presence of ADP, the motor domain of kinesin, still bound to the microtubule, adopts a previously undescribed, highly mobile state. This state may be general to the chemomechanical cycle of motor proteins; in the case of kinesin, the transition from a highly mobile to a rigid state after ADP release may contribute to the generation of the 8 nm step.
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PMID:ADP-induced rocking of the kinesin motor domain revealed by single-molecule fluorescence polarization microscopy. 1137 8

Kinesin motors are specialized enzymes that use hydrolysis of ATP to generate force and movement along their cellular tracks, the microtubules. Although numerous biochemical and biophysical studies have accumulated much data that link microtubule-assisted ATP hydrolysis to kinesin motion, the structural view of kinesin movement remains unclear. This study of the monomeric kinesin motor KIF1A combines X-ray crystallography and cryo-electron microscopy, and allows analysis of force-generating conformational changes at atomic resolution. The motor is revealed in its two functionally critical states-complexed with ADP and with a non-hydrolysable analogue of ATP. The conformational change observed between the ADP-bound and the ATP-like structures of the KIF1A catalytic core is modular, extends to all kinesins and is similar to the conformational change used by myosin motors and G proteins. Docking of the ADP-bound and ATP-like crystallographic models of KIF1A into the corresponding cryo-electron microscopy maps suggests a rationale for the plus-end directional bias associated with the kinesin catalytic core.
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PMID:Switch-based mechanism of kinesin motors. 1137 68

Molecular motors move along actin or microtubules by rapidly hydrolyzing ATP and undergoing changes in filament-binding affinity with steps of the nucleotide hydrolysis cycle. It is generally accepted that motor binding to its filament greatly increases the rate of ATP hydrolysis, but the structural changes in the motor associated with ATPase activation are not known. To identify the conformational changes underlying motor movement on its filament, we solved the crystal structures of three kinesin mutants that decouple nucleotide and microtubule binding by the motor, and block microtubule-activated, but not basal, ATPase activity. Conformational changes in the structures include a disordered loop and helices in the switch I region and a visible switch II loop, which is disordered in wild-type structures. Switch I moved closer to the bound nucleotide in two mutant structures, perturbing water-mediated interactions with the Mg2+. This could weaken Mg2+ binding and accelerate ADP release to activate the motor ATPASE: The structural changes we observe define a signaling pathway within the motor for ATPase activation that is likely to be essential for motor movement on microtubules.
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PMID:A structural pathway for activation of the kinesin motor ATPase. 1138 96

Recent experiments, drawing upon single-molecule, solution kinetic and structural techniques, have clarified our mechanistic understanding of class V myosins. The findings of the past two years can be summarized as follows: (1) Myosin V is a highly efficient processive motor, surpassing even conventional kinesin in the distance that individual molecules can traverse. (2) The kinetic scheme underlying ATP turnover resembles those of myosins I and II but with rate constants tuned to favor strong binding to actin. ADP release precedes dissociation from actin and is rate-limiting in the cycle. (3) Myosin V walks in strides averaging approximately 36 nm, the long pitch pseudo-repeat of the actin helix, each step coupled to a single ATP hydrolysis. Such a unitary displacement, the largest molecular step size measured to date, is required for a processive myosin motor to follow a linear trajectory along a helical actin track.
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PMID:Myosin learns to walk. 1149 35

We determined the crystal structure of the motor domain of the fast fungal kinesin from Neurospora crassa (NcKin). The structure has several unique features. (i) Loop 11 in the switch 2 region is ordered and enables one to describe the complete nucleotide-binding pocket, including three inter-switch salt bridges between switch 1 and 2. (ii) Loop 9 in the switch 1 region bends outwards, making the nucleotide-binding pocket very wide. The displacement in switch 1 resembles that of the G-protein ras complexed with its guanosine nucleotide exchange factor. (iii) Loop 5 in the entrance to the nucleotide-binding pocket is remarkably long and interacts with the ribose of ATP. (iv) The linker and neck region is not well defined, indicating that it is mobile. (v) Image reconstructions of ice-embedded microtubules decorated with NcKin show that it interacts with several tubulin subunits, including a central beta-tubulin monomer and the two flanking alpha-tubulin monomers within the microtubule protofilament. Comparison of NcKin with other kinesins, myosin and G-proteins suggests that the rate-limiting step of ADP release is accelerated in the fungal kinesin and accounts for the unusually high velocity and ATPase activity.
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PMID:Structure of a fast kinesin: implications for ATPase mechanism and interactions with microtubules. 1170 93

Kinesins are microtubule-dependent motors that serve a multitude of cellular purposes. The conserved motor domain provides the energy required for these processes. Shortly after the solution of the first kinesin motor domain crystal structures the similarity to myosin and G-proteins was noted. By analogy, it was suspected that regions flanking the gamma-phosphate group of the nucleotide (in particular the so-called switch I and II regions) play important roles in the catalytic mechanism and the communication between the nucleotide cleft and the microtubule binding site. Since then, mutational analyses have supported this notion. Moreover, additional high-resolution structures have demonstrated that the switch regions can assume variable conformations. In one case, a comparison of an ADP state and an ATP-like state indicates a crucial involvement of the helix flanking switch II in modulating microtubule affinity. High-resolution structures of a kinesin-related protein mutated in the switch regions confirm the correlation between structural features in the switch vicinity and coupling of microtubule binding and nucleotide state.
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PMID:A look into kinesin's powerhouse. 1172 37

New crystal structures of the kinesin motors differ from previously described motor-ADP atomic models, showing striking changes both in the switch I region near the nucleotide-binding cleft and in the switch II or 'relay' helix at the filament-binding face of the motor. The switch I region, present as a short helix flanked by two loops in previous motor-ADP structures, rearranges into a pseudo-beta-hairpin or is completely disordered with melted helices to either side of the disordered switch I loop. The relay helix undergoes a rotational movement coupled to a translation that differs from the piston-like movement of the relay helix observed in myosin. The changes observed in the crystal structures are interpreted to represent structural transitions that occur in the kinesin motors during the ATP hydrolysis cycle. The movements of switch I residues disrupt the water-mediated coordination of the bound Mg2+, which could result in loss of Mg2+ and ADP, raising the intriguing possibility that disruption of the switch I region leads to release of nucleotide by the kinesins. None of the new structures is a true motor-ATP state, however, probably because conformational changes at the active site of the kinesins require interactions with microtubules to stabilize the movements.
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PMID:Kinesin: switch I & II and the motor mechanism. 1180 20

The hand-over-hand stepping mechanism of kinesin at low loads is inadequately understood because the number of molecular steps taken per encounter with the microtubule is difficult to measure: optical traps do not register steps at zero load, while evanescent wave microscopy of single molecules of GFP-kinesin suffers from premature photobleaching. Obtaining low-load data is important because it can efficiently distinguish between alternative proposed mechanisms for molecular walking. We report a novel experiment that records the missing data. We fused kinesin to gelsolin, creating a construct that severs and caps rhodamine-phalloidin actin filaments, setting exactly one kinesin molecule on one end of each fluorescent actin filament. Single kinesin molecules labeled in this way can be tracked easily and definitively using a standard epifluorescence microscope. We use the new system to show that, contrary to a recent report, kinesin run length at low load is independent of ATP concentration in the muM to mM range of ATP concentration. Adding competitor ADP in the presence of saturating ATP decreases both velocity and run length. Based on these data, we propose a simplified model for the mechanism of processive stepping.
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PMID:Direct long-term observation of kinesin processivity at low load. 1186 70


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