Two independent mechanical events in the interaction cycle of skeletal muscle myosin with actin

Year: 2006

Authors: Capitanio M., Canepari, M., Cacciafesta P., Lombardi V., Cicchi R., Maffei M., Pavone F.S., Bottinelli R.

Autors Affiliation: European Laboratory for Non-linear Spectroscopy, University of Florence, Via Nello Carrara 1, 50019 Sesto Fiorentino, Firenze, Italy;
Department of Experimental Medicine, Human Physiology Unit, University of Pavia, Via Forlanini 6, 27100 Pavia, Italy;
Laboratory of Physiology, Dipartimento di Biologia Animale e Genetica, University of Florence, Via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy;
Department of Physics, University of Florence, Via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy

Abstract: During skeletal muscle contraction, regular arrays of actin and myosin filaments slide past each other driven by the cyclic ATP-dependent interaction of the motor protein myosin II (the cross-bridge) with actin. The rate of the cross-bridge cycle and its load-dependence, defining shortening velocity and energy consumption at the molecular level, vary widely among different isoforms of myosin II. However, the underlying mechanisms remain poorly understood. We have addressed this question by applying a single-molecule approach to rapidly (approximate to 300 mu s) and precisely (approximate to 0.1 nm) detect acto-myosin interactions of two myosin isoforms having large differences in shortening velocity. We show that skeletal myosin propels actin filaments, performing its conformational change (working stroke) in two steps. The first step (approximate to 3.4-5.2 nm) occurs immediately after myosin binding and is followed by a smaller step (approximate to 1.0-1.3 nm), which occurs much faster in the fast myosin isoform than in the slow one, independently of ATP concentration. On the other hand, the rate of the second phase of the working stroke, from development of the latter step to dissociation of the acto-myosin complex, is very similar in the two isoforms and depends linearly on ATP concentration. The finding of a second mechanical event in the working stroke of skeletal muscle myosin provides the molecular basis for a simple model of actomyosin interaction. This model can account for the variation, in different fiber types, of the rate of the cross-bridge cycle and provides a common scheme for the chemo-mechanical transduction within the myosin family.


Volume: 103 (1)      Pages from: 87  to: 92

KeyWords: actin; adenosine triphosphate; myosin, actin filament; animal tissue; article; gastrocnemius muscle; kinetics; leg muscle; male; mechanotransduction; mouse; muscle cell; muscle contraction; nonhuman; priority journal; rat; skeletal muscle; velocity, Actins; Adenosine Triphosphate; Animals; Biomechanics; Biophysics; Computer Simulation; Kinetics; Male; Models, Biological; Muscle Contraction; Muscle, Skeletal; Myosins; Rats; Rats, Wistar; Time Factors, Animalia
DOI: 10.1073/pnas.0506830102

Citations: 129
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