Propagation of a signal coordinating force generation along an actin filament in actomyosin complexes

doi:10.1016/S0301-4622(98)00184-7

Biophysical Chemistry

Volume 75, Issue 2, 16 November 1998, Pages 81-85

https://doi.org/10.1016/S0301-4622(98)00184-7 Get rights and content

Abstract

Force generation due to ATP hydrolysis by myosin molecules contacting an actin filament was found to be coordinated along the filament. We marked several points along the actin filament with the aid of a fluorescent material, and measured the temporal development of the acceleration of each marked point in the stationary coordinate space. Variations in the acceleration of the sliding movement of the actin filament propagated backward along the filament. Variations in the acceleration propagating in the direction opposite to the direction of the sliding movement show that force generation at each active site of an actomyosin complex could be regulated in a communicative manner along the actin filament.

Introduction

ATP hydrolysis due to myosin molecules contacting an actin filament asks the intriguing question of how each myosin molecule would start hydrolyzing an ATP molecule in relation to the similar hydrolysis proceeding in its neighborhood 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. If each myosin molecule contacting the actin filament hydrolyzes ATP molecules in a manner totally independent of other neighboring myosin molecules contacting the filament, it would be hard to actualize a seemingly uniform sliding movement of the filament on myosin molecules. The absence of any coordination among the myosin molecules contacting the actin filament with regard to their ATP hydrolysis would disturb a proper functioning of the sliding movement. In the absence of such a coordination, the phase of each actin-activated ATP hydrolysis cycle of a myosin molecule could be random among themselves, with disturbing consequences upon the coordination of force generations along the filament. Unless proper coordination is available for the force generations along the filament, there would be no coherent supra-molecular movement of an actin filament relative to the contacting myosin molecules. At issue should be to see how such a coordination could be established in reality.

We examined how an actin filament would develop its sliding movement longitudinally as interacting with myosin molecules in the presence of ATP molecules, and measured variations in the accelerations of several marked points along the filament. Each marker along the filament denoted as a speckle was a fluorescent material attached to the filament. We prepared a speckled actin filament for the purpose. Although variations in the acceleration of a marked point put on the actin filament are only indirectly related to the force generation proceeding there, the observed variations revealed how the actin filament comes to establish a coordination of the acceleration along the filament.

Section snippets

How to prepare a speckled actin filament?

Actin and myosin molecules were prepared from rabbit skeletal muscle 12, 13, 14. Speckled actin filaments were made from a mixture of actin filaments, both unlabeled and labeled by rhodamine–phalloidine. Unlabeled and labeled actin filaments [25 mM KCl, 25 mM imidazole-HCl (pH=7.4), 4 mM MgCl₂, 1 mM DTT] were made and treated with equal molar phalloidin, and their concentrations were maintained at 33 μg/ml. The mixture of the suspensions of labeled and unlabeled actin filaments with a volume

Results and discussion

We first observed how each speckle on the actin filament moved in the stationary coordinate space as demonstrated in Fig. 1, in which we fabricated five speckles on a single actin filament. The spacing between the neighboring speckles was greater than 1 μm. The traces of the movements of two marked points, speckle p1 situated near at the pointed-end of the actin filament and speckle p5 near at the barbed-end, recorded on the stationary coordinate space, are displayed in Fig. 2. The observation

Concluding remarks

Needless to say, each actomyosin complex along an actin filament is instrumental for the generation of the force responsible for the sliding movement. In this regard, there are at least two processes proceeding in a mutually coordinated manner. One is the unit process of the hydrolysis of an ATP molecule at each actomyosin complex, and the other is the communication or coordination of the unit processes between the neighboring actomyosin complexes along the filament 3, 16. We have concerned

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LetterPropagation of a signal coordinating force generation along an actin filament in actomyosin complexes

Abstract

Introduction

Section snippets

How to prepare a speckled actin filament?

Results and discussion

Concluding remarks

Biophys. Chem.

Biophys. Chem.

Biophys. Chem.

Biophys. J.

Biophys. Chem.

Biophys. J.

Biophys. J.

J. Biol. Chem.

Letter
Propagation of a signal coordinating force generation along an actin filament in actomyosin complexes