scholarly journals Kinematics of the Lever Arm Swing in Myosin VI

2016 ◽  
Author(s):  
M. L. Mugnai ◽  
D. Thirumalai
Keyword(s):  
Rotational Diffusion ◽  
Quantitative Agreement ◽  
Motor Domain ◽  
Coarse Grained ◽  
Power Stroke ◽  
Myosin Vi ◽  
Step Size ◽  
Arm Swing ◽  
Post Stroke ◽  
Lever Arm

AbstractMyosin VI (MVI) is the only known member of the myosin superfamily that, upon dimerization, walks processively towards the pointed end of the actin filament. The leading head of the dimer directs the trailing head forward with a power stroke, a conformational change of the motor domain exaggerated by the lever arm. Using a new coarse-grained model for the power stroke of a single MVI, we provide the molecular basis for its motility. We show that the power stroke occurs in two major steps: first, the motor domain attains the post-stroke conformation without directing the lever arm forward; second, the lever arm reaches the post-stroke orientation by undergoing a rotational diffusion. From the analysis of the trajectories, we discover that the potential that directs the rotating lever arm towards the post-stroke conformation is almost flat, implying that the lever arm rotation is mostly un-coupled from the motor domain. Because a backward load comparable with the largest inter-head tension in a MVI dimer prevents the rotation of the lever arm, our model suggests that the leading-head lever arm of a MVI dimer is uncoupled, in accord with the inference drawn from polarized Total Internal Reflection Fluorescence (polTIRF) experiments. Our simulations are in quantitative agreement with polTIRF experiments, which validates our structural insights. Finally, we discuss the implications of our model in explaining the broad step-size distribution of MVI stepping pattern, and we make testable predictions.

scholarly journals Kinematics of the lever arm swing in myosin VI

2017 ◽  
Vol 114 (22) ◽  
pp. E4389-E4398 ◽  
Author(s):  
Mauro L. Mugnai ◽  
D. Thirumalai
Keyword(s):  
Rotational Diffusion ◽  
Quantitative Agreement ◽  
Motor Domain ◽  
Coarse Grained ◽  
Power Stroke ◽  
Myosin Vi ◽  
Step Size ◽  
Arm Swing ◽  
Coarse Grained Model ◽  
Lever Arm

Myosin VI (MVI) is the only known member of the myosin superfamily that, upon dimerization, walks processively toward the pointed end of the actin filament. The leading head of the dimer directs the trailing head forward with a power stroke, a conformational change of the motor domain exaggerated by the lever arm. Using a unique coarse-grained model for the power stroke of a single MVI, we provide the molecular basis for its motility. We show that the power stroke occurs in two major steps. First, the motor domain attains the poststroke conformation without directing the lever arm forward; and second, the lever arm reaches the poststroke orientation by undergoing a rotational diffusion. From the analysis of the trajectories, we discover that the potential that directs the rotating lever arm toward the poststroke conformation is almost flat, implying that the lever arm rotation is mostly uncoupled from the motor domain. Because a backward load comparable to the largest interhead tension in a MVI dimer prevents the rotation of the lever arm, our model suggests that the leading-head lever arm of a MVI dimer is uncoupled, in accord with the inference drawn from polarized total internal reflection fluorescence (polTIRF) experiments. Without any adjustable parameter, our simulations lead to quantitative agreement with polTIRF experiments, which validates the structural insights. Finally, in addition to making testable predictions, we also discuss the implications of our model in explaining the broad step-size distribution of the MVI stepping pattern.

scholarly journals Different degrees of lever arm rotation control myosin step size

2003 ◽  
Vol 161 (2) ◽  
pp. 237-241 ◽  
Author(s):  
Danny Köhler ◽  
Christine Ruff ◽  
Edgar Meyhöfer ◽  
Martin Bähler
Keyword(s):  
Light Chain ◽  
Structural Changes ◽  
Quantitative Agreement ◽  
Linear Increase ◽  
Binding Domain ◽  
Motor Domain ◽  
Step Size ◽  
The Core ◽  
Lever Arm ◽  
Head Domain

Myosins are actin-based motors that are generally believed to move by amplifying small structural changes in the core motor domain via a lever arm rotation of the light chain binding domain. However, the lack of a quantitative agreement between observed step sizes and the length of the proposed lever arms from different myosins challenges this view. We analyzed the step size of rat myosin 1d (Myo1d) and surprisingly found that this myosin takes unexpectedly large steps in comparison to other myosins. Engineering the length of the light chain binding domain of rat Myo1d resulted in a linear increase of step size in relation to the putative lever arm length, indicative of a lever arm rotation of the light chain binding domain. The extrapolated pivoting point resided in the same region of the rat Myo1d head domain as in conventional myosins. Therefore, rat Myo1d achieves its larger working stroke by a large calculated ∼90° rotation of the light chain binding domain. These results demonstrate that differences in myosin step sizes are not only controlled by lever arm length, but also by substantial differences in the degree of lever arm rotation.

scholarly journals Parsing the roles of neck-linker docking and tethered head diffusion in the stepping dynamics of kinesin

2017 ◽  
Author(s):  
Zhechun Zhang ◽  
Yonathan Goldtzvik ◽  
D. Thirumalai
Keyword(s):  
Conformational Changes ◽  
Critical Role ◽  
Molecular Simulations ◽  
Single Step ◽  
Motor Domain ◽  
Coarse Grained ◽  
Power Stroke ◽  
Stochastic Motion ◽  
Correct Orientation ◽  
Motor Head

Kinesin walks processively on microtubules (MTs) in an asymmetric hand-over-hand manner consuming one ATP molecule per 16 nm step. The contributions due to docking of the approximately thirteen residue neck linker to the leading head (deemed to be the power stroke), and diffusion of the trailing head contribute in propelling the motor by 16 nm have not been quantified. We use molecular simulations by creating a new coarse-grained model of the microtubule-kinesin complex, which reproduces the measured stall force as well as the force required to dislodge the motor head from the MT, to show that nearly three quarters of the step occurs by bidirectional stochastic motion of the TH. However, docking of the neck linker to the leading head constrains the extent of diffusion and minimizes the probability that kinesin takes side steps implying that both the events are necessary in the motility of kinesin, and for the maintenance of processivity. Surprisingly, we find that during a single step the trailing head stochastically hops multiple times between the geometrically accessible neighboring sites on the MT prior to forming a stable interaction with the target binding site with correct orientation between the motor head and the α/ß tubulin dimer.Significance StatementLike all motors, the stepping of the two headed conventional Kinesin on the microtubule is facilitated by conformational changes in the motor domain upon ATP binding and hydrolysis. Numerous experiments have revealed that docking of the thirteen residue neck linker (NL) to the motor domain of the leading plays a critical role in propelling the trailing head towards the plus end of the microtubule by nearly 16 nm in a single step. Surprisingly our molecular simulations reveal that nearly three quarters of the step occurs by stochastic diffusion of the trailing head. Docking of the NL restricts the extent of diffusion, thus forcing the motor to walk with overwhelming probability on a single protofilament of the MT.

scholarly journals Direct measurements of the coordination of lever arm swing and the catalytic cycle in myosin V

2015 ◽  
Vol 112 (47) ◽  
pp. 14593-14598 ◽  
Author(s):  
Darshan V. Trivedi ◽  
Joseph M. Muretta ◽  
Anja M. Swenson ◽  
Jonathon P. Davis ◽  
David D. Thomas ◽  
...  
Keyword(s):  
Atp Hydrolysis ◽  
Arm Movement ◽  
Power Stroke ◽  
Release Time ◽  
Slow Step ◽  
Myosin V ◽  
Time Resolved ◽  
Arm Swing ◽  
Structural Mechanism ◽  
Lever Arm

Myosins use a conserved structural mechanism to convert the energy from ATP hydrolysis into a large swing of the force-generating lever arm. The precise timing of the lever arm movement with respect to the steps in the actomyosin ATPase cycle has not been determined. We have developed a FRET system in myosin V that uses three donor–acceptor pairs to examine the kinetics of lever arm swing during the recovery and power stroke phases of the ATPase cycle. During the recovery stroke the lever arm swing is tightly coupled to priming the active site for ATP hydrolysis. The lever arm swing during the power stroke occurs in two steps, a fast step that occurs before phosphate release and a slow step that occurs before ADP release. Time-resolved FRET demonstrates a 20-Å change in distance between the pre- and postpower stroke states and shows that the lever arm is more dynamic in the postpower stroke state. Our results suggest myosin binding to actin in the ADP.Pi complex triggers a rapid power stroke that gates the release of phosphate, whereas a second slower power stroke may be important for mediating strain sensitivity.

scholarly journals Dynamics of Allosteric Transitions in Dynein

2018 ◽  
Author(s):  
Yonathan Goldtzvik ◽  
Mauro L. Mugnai ◽  
D. Thirumalai
Keyword(s):  
Conformational Changes ◽  
Cytoplasmic Dynein ◽  
Motor Domain ◽  
Coarse Grained ◽  
Power Stroke ◽  
Coarse Grained Model ◽  
Multiple Routes ◽  
Adp Release ◽  
Mechanical Element ◽  
Allosteric Transitions

1SummaryCytoplasmic Dynein, a motor with an unusual architecture made up of a motor domain belonging to the AAA+ family, walks on microtubule towards the minus end. Prompted by the availability of structures in different nucleotide states, we performed simulations based on a new coarse-grained model to illustrate the molecular details of the dynamics of allosteric transitions in the motor. The simulations show that binding of ATP results in the closure of the cleft between the AAA1 and AAA2, which in turn triggers conformational changes in the rest of the motor domain, thus poising dynein in the pre-power stroke state. Interactions with the microtubule, which are modeled implicitly, substantially enhances the rate of ADP release, and formation of the post-power stroke state. The dynamics associated with the key mechanical element, the linker (LN) domain, which changes from a straight to a bent state and vice versa, are highly heterogeneous suggestive of multiple routes in the pre power stroke to post power stroke transition. We show that persistent interactions between the LN and the insert loops in the AAA2 domain prevent the formation of pre-power stroke state when ATP is bound to AAA3, thus locking dynein in a non-functional repressed state. Motility in such a state may be rescued by applying mechanical force to the LN domain. Taken together, these results show how the intricate signaling dynamics within the motor domain facilitate the stepping of dynein.

scholarly journals Myosin VI undergoes a 180  power stroke implying an uncoupling of the front lever arm

2009 ◽  
Vol 106 (43) ◽  
pp. 18255-18260 ◽  
Author(s):  
J. G. Reifenberger ◽  
E. Toprak ◽  
H. Kim ◽  
D. Safer ◽  
H. L. Sweeney ◽  
...  
Keyword(s):  
Power Stroke ◽  
Myosin Vi ◽  
Lever Arm

scholarly journals Kinematics of the Lever Arm Swing in Myosin VI

2017 ◽  
Vol 112 (3) ◽  
pp. 265a
Author(s):  
Mauro L. Mugnai ◽  
Dave Thirumalai
Keyword(s):  
Myosin Vi ◽  
Arm Swing ◽  
Lever Arm

Visualizing myosin's power stroke in muscle contraction

2000 ◽  
Vol 113 (20) ◽  
pp. 3551-3562
Author(s):  
M.C. Reedy
Keyword(s):  
Catalytic Domain ◽  
Insect Flight ◽  
Actin Binding ◽  
Power Stroke ◽  
X Ray Diffraction ◽  
Motor Action ◽  
Arm Swing ◽  
Lever Arm ◽  
Total Interaction

The long-standing swinging crossbridge or lever arm hypothesis for the motor action of myosin heads finds support in recent results from 3-D tomograms of insect flight muscle (IFM) fast frozen during active contraction and from both fluorescence polarization and X-ray diffraction during rapid stretches or releases of isometrically contracting fibers. The latter provide direct evidence for lever arm movements synchronous with force changes. Rebuilding the atomic model of nucleotide-free subfragment 1 (S1) to fit fast-frozen, active IFM crossbridges suggests a two-stage power stroke in which the catalytic domain rolls on actin from weak to strong binding; this is followed by a 5-nm lever arm swing of the light chain domain, which gives a total interaction distance of approx. 12 nm. Comparison of S1 crystal structures with in situ myosin heads suggests that actin binding may be necessary in order to view the full repertoire of myosin motor action. The differing positions of the catalytic domains of actin-attached myosin heads in contracting IFM suggest that both the actin-myosin binding energy and the hydrolysis of ATP may be used to cock the crossbridge and drive the power stroke.

Novel configuration of a myosin II transient intermediate analogue revealed by quick-freeze deep-etch replica electron microscopy

2013 ◽  
Vol 450 (1) ◽  
pp. 23-35 ◽  
Author(s):  
Yoshitaka Kimori ◽  
Norio Baba ◽  
Eisaku Katayama
Keyword(s):  
Electron Microscopy ◽  
Catalytic Domain ◽  
Three Dimensional ◽  
Power Stroke ◽  
Structural Analogue ◽  
Unusual Structure ◽  
Mapping Procedure ◽  
Cross Bridge ◽  
Lever Arm ◽  
Transient Intermediate

In the present paper, we described our attempt to characterize the rough three-dimensional features of the structural analogue of the key intermediate of myosin's cross-bridge cycle. Using quick-freeze deep-etch replica electron microscopy, we observed that actin-attached myosin during in vitro sliding was bent superficially as postulated by the conventional hypothesis, but in the opposite direction of the putative pre-power-stroke configuration, as for ADP·Vi (inorganic vanadate)-bound myosin. We searched for the conformational species with a similar appearance and found that SH1–SH2 (thiols 1 and 2)-cross-linked myosin is a good candidate. To characterize such small asymmetric structures, we employed a new pattern-recognition procedure that accommodates the metal-replicated samples. In this method, the best-matched views of the target microscopic images were selected from a comprehensive set of images simulated from known atomic co-ordinates of relevant proteins. Together with effective morphological filtering, we could define the conformational species and the view angles of the catalytic domain and the lever arm cropped from averaged images of disulfide-cross-linked myosin. Whereas the catalytic domain of the new conformer closely resembled the pPDM (N,N′-p-phenylenedimaleimide)-treated, but SH2 Lys705-cross-linked, structure (PDB code 1L2O), a minor product of the same cross-linking reaction, the lever arm projected differently. Using separately determined view angles of the catalytic domain and the lever arm, we built a model of disulfide-cross-linked myosin. Further combination with the ‘displacement-mapping’ procedure enabled us to reconstruct the global three-dimensional envelope of the unusual structure whose lever arm orientation is compatible with our reports on the actin-sliding cross-bridge structure. Assuming this conformer as the structural analogue of the transient intermediate during actin sliding, the power stroke of the lever arm might accompany the reversal of the disorganized SH1 helix.

Optical vs. chemical driving for molecular machines

2016 ◽  
Vol 195 ◽  
pp. 583-597 ◽  
Author(s):  
R. D. Astumian
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Thermodynamic Parameters ◽  
Energy Surface ◽  
Molecular Machines ◽  
Coarse Grained ◽  
Power Stroke ◽  
Microscopic Reversibility ◽  
Single Time ◽  
External Modulation

Molecular machines use external energy to drive transport, to do mechanical, osmotic, or electrical work on the environment, and to form structure. In this paper the fundamental difference between the design principles necessary for a molecular machine to use light or external modulation of thermodynamic parameters as an energy sourcevs.the design principle for using an exergonic chemical reaction as a fuel will be explored. The key difference is that for catalytically-driven motors microscopic reversibility must hold arbitrarily far from equilibrium. Applying the constraints of microscopic reversibility assures that a coarse grained model is consistent with an underlying model for motion on a single time-independent potential energy surface. In contrast, light-driven processes, and processes driven by external modulation of the thermodynamic parameters of a system cannot in general be described in terms of motion on a single time-independent potential energy surface, and the rate constants are not constrained by microscopic reversibility. The results presented here call into question the value of the so-called power stroke model as an explanation of the function of autonomous chemically-driven molecular machines such as are commonly found in biology.

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