Emerging complex pathways of the actomyosin powerstroke

Málnási‐Csizmadia, András; Kovács, Mihály

doi:10.1016/j.tibs.2010.07.012

Cited by 48 publications

(62 citation statements)

References 50 publications

(63 reference statements)

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“…1A) has been shown to be a nonequilibrium process (discussed in detail in ref. 28). Nevertheless, the present coupling model helps to understand how myosin controls rebinding to F actin after step III → III 0 .…”

Section: Discussionmentioning

confidence: 87%

Structural mechanism of the ATP-induced dissociation of rigor myosin from actin

Kühner

Fischer

2011

Proc. Natl. Acad. Sci. U.S.A.

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Myosin is a true nanomachine, which produces mechanical force from ATP hydrolysis by cyclically interacting with actin filaments in a four-step cycle. The principle underlying each step is that structural changes in separate regions of the protein must be mechanically coupled. The step in which myosin dissociates from tightly bound actin (the rigor state) is triggered by the 30 Å distant binding of ATP. Large conformational differences between the crystal structures make it difficult to perceive the coupling mechanism. Energetically accessible transition pathways computed at atomic detail reveal a simple coupling mechanism for the reciprocal binding of ATP and actin.chemomechanical coupling | conformational transition | conjugate peak refinement | muscle contraction | power-stroke M otility as well as intracellular transport are essential functions in all organisms, from unicellulars to highest eukaryotes. They are driven by molecular motors, which convert the chemical energy of ATP hydrolysis into mechanical force (1). One family of motors are myosins, which drive processes like cytokinesis, vesicle transport, and muscle contraction by walking along actin fibrils (2).The N-terminal globular domain of myosin (called the head) contains all the functional domains (i.e., the ATP binding site, the actin-binding regions, and the rotating "converter" domain). It is able to hydrolyze ATP and move along an actin filament on its own (3). The cyclic interaction of myosin and actin to create motion is known as the Lymn-Taylor cycle (4) (Fig. 1A). The principle underlying each of the four Lymn-Taylor steps is that structural change in one region of the protein is tightly coupled to change in another domain of the protein. This sort of welldefined coupling between parts of the motor really is the essence of any type of motor (for instance, the motions of the valve and the piston are coupled in a car engine). The key to understanding how myosin works as a nanomachine is to understand in each Lymn-Taylor step how the structural information is communicated from one part of myosin to another (much like finding the crankshaft and the timing belt in the engine analogy).The focus here is on the rigor-dissociation step (Fig. 1A, I → II), in which, upon binding ATP, the head dissociates from the actin fibril and goes from the rigor state (thus called for the stiffness of corpses when ATP gets depleted in muscle cells) to the prerecovery (also known as postrigor) state (kinetic relaxation time approximately 10 ms in excess ATP; ref. 5). In this step, small changes in the ATP binding site are coupled to large structural changes in the 30-Å distant actin-binding domain that substantially reduce binding affinity for actin (6, 7), thus leading to the dissociation. We describe that mechanism at atomic detail using simulations of the conformational transition between the rigor and the postrigor states and present molecular movies of the energetically accessible transition pathways (SI Text). Fig. 1B shows the rigor-like crystal structure of...

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Section: Discussionmentioning

confidence: 87%

Structural mechanism of the ATP-induced dissociation of rigor myosin from actin

Kühner

Fischer

2011

Proc. Natl. Acad. Sci. U.S.A.

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“…However, the assignment of these trapped nucleotide analog states to specific biochemical intermediates in the kinetic cycle is uncertain. Analysis of myosin's intrinsic fluorescence kinetics does suggest a branched mechanism of myosin-nucleotide interaction with two structurally different intermediates (5,6,17,24), but this method does not have the structural resolution of TR-FRET. In order to obtain simultaneous structural and kinetic resolution, the present study uses ðTRÞ 2 FRET (performing a complete TR-FRET experiment every 0.1 ms) to determine directly the structural kinetics within the myosin force-generating region during the myosin-ATP interaction and the recovery stroke (steps 1 and 2, Scheme 1 and Fig.…”

mentioning

confidence: 99%

Structural kinetics of myosin by transient time-resolved FRET

Nesmelov

Agafonov

Negrashov

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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For many proteins, especially for molecular motors and other enzymes, the functional mechanisms remain unsolved due to a gap between static structural data and kinetics. We have filled this gap by detecting structure and kinetics simultaneously. This structural kinetics experiment is made possible by a new technique, ðTRÞ 2 FRET (transient time-resolved FRET), which resolves protein structural states on the submillisecond timescale during the transient phase of a biochemical reaction. ðTRÞ 2 FRET is accomplished with a fluorescence instrument that uses a pulsed laser and direct waveform recording to acquire an accurate subnanosecond timeresolved fluorescence decay every 0.1 ms after stopped flow. To apply this method to myosin, we labeled the force-generating region site specifically with two probes, mixed rapidly with ATP to initiate the recovery stroke, and measured the interprobe distance by ðTRÞ 2 FRET with high resolution in both space and time. We found that the relay helix bends during the recovery stroke, most of which occurs before ATP is hydrolyzed, and two structural states (relay helix straight and bent) are resolved in each nucleotide-bound biochemical state. Thus the structural transition of the force-generating region of myosin is only loosely coupled to the ATPase reaction, with conformational selection driving the motor mechanism.disorder-to-order transition | myosin II | dictyostelium S tructural dynamics lies at the heart of protein function. Transitions among distinct structural states, each characterized by both structural order and internal dynamic disorder, are typically required for the function of a protein, especially an enzyme. To describe the mechanism of a protein's function is to describe its structural kinetics, i.e., the coupling of protein structural transitions to biochemical kinetics, as defined by changes in bound ligand (1-3). However, for most proteins there remains mechanistic ambiguity due to a gap between structural data, determined primarily from static protein crystals, and kinetics, measured during the transient phase of the biochemical reaction. In the present study, we have closed this gap by measuring structure and kinetics simultaneously, using myosin as a powerful example.In a molecular motor, ATP binding and hydrolysis initiate protein structural changes that lead to force generation, and characterization of motor protein structural kinetics is essential to understand the protein in action. Myosin is a molecular motor responsible for actin-dependent force generation and movement in muscle and nonmuscle cells; it works cyclically, producing mechanical work on actin using energy from ATP hydrolysis (recently reviewed in refs. 4 and 5). Transient kinetics in myosin has been typically monitored by tryptophan fluorescence (6, 7), but that signal provides no direct structural information. FRET does provide structural information, in the form of interprobe distance, and transient FRET experiments have provided a glimpse of structural kinetics in muscle and other protein...

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“…We assume that this circle can slide without friction inside the cleft, but always remains in contact with the U50 and L50 subdomains. This circle imitates the effect of a water droplet inside the cleft, whose existence we assume based on observations [9]. Due to the hydrophobicity of myosin II it tries to reduce its surface exposed to water molecules, hence the cleft favors being closed.…”

Section: Mechanical Model Of Myosin IImentioning

confidence: 94%

“…The U50 and L50 subdomains can move relative to each other, they can open up or close the gap between them depending on the actual phase during the four strokes. Within the motor domain, other subdomains can be identified [8,9], like the N-terminal subdomain that seems to serve as a support for all other subdomains, the converter domain providing the large displacement of the lever arm, and the relay helix which we identify as the internal lever arm for our model. It has been observed [2,9,10] that the relay helix shows a seesaw motion during the enzymatic cycle, which is closely coupled with the opening and closing of the cleft.…”

Section: Introductionmentioning

confidence: 97%

“…This shows that thermal forces are indeed important, hence in this paper we extend our previous model [4] by incorporating the effects of random thermal forces. Recent experimental techniques provide a quite detailed picture of the main elements that build up myosin II [8,9]. Within the motor domain, several subdomains have been revealed, which seem to keep their shape during the four strokes of myosin II motion, but whose relative position seems to be changing.…”

Section: Introductionmentioning

confidence: 99%

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