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Actin and Myosin in Muscle Contraction

Actin and Myosin in Muscle Contraction

Actin and myosin are contractile proteins that form the sarcomere found in skeletal muscle tissues for regulating muscle contraction. Actin, a globular contractile protein, interacts with myosin for muscle contraction. The skeletal tissue appears striped or striated under a microscope due to the repeated arrangement of contractile proteins actin and myosin along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes...

ATP Synthase: Mechanism

ATP Synthase: Mechanism

In animals, the mitochondrial F1F0 ATP synthase is the key protein that synthesizes ATP molecules through a complex catalytic mechanism. While the nuclear genome encodes the majority of ATP synthase subunits, the mitochondrial genome encodes some of the enzyme's most critical components. The formation of this multi-subunit enzyme is a complex multi-step process regulated at the level of transcription, translation, and assembly. Defects in one or more of these steps can result in decreased ATP...

Cross-bridge Cycle

Cross-bridge Cycle

As muscle contracts, the overlap between the thin and thick filaments increases, decreasing the length of the sarcomere—the contractile unit of the muscle—using energy in the form of ATP. At the molecular level, this is a cyclic, multistep process that involves binding and hydrolysis of ATP, and movement of actin by myosin.

The Role of Actin and Myosin in Non-muscle Cells

The Role of Actin and Myosin in Non-muscle Cells

Actin and myosin or actomyosin filaments also play a significant role in cells other than those involved in muscle contraction (which occurs within the sarcomere of muscle cells). The mechanism of non-muscle cell contractile bundles was first observed in Dictyostelium and Acanthamoeba. In non-muscle cells, two bundles are commonly found: stress fibers and actomyosin adherence belts. These contractile bundles are smaller and less organized than the ones found in muscle cells. They are held...

Overview of Myosin Structure and Function

Overview of Myosin Structure and Function

Myosins are a family of molecular motor proteins, first identified in the skeletal muscles, where they are responsible for muscle contraction. Along with their role in muscle contraction, these proteins also play a role in the intracellular transport of molecules and vesicles. There are twenty-four classes of myosins based on their domain sequence and organization. Of the twenty-four, six classes (Myosin I, Myosin II, Myosin V, Myosin VI, Myosin VII, and Myosin X) have been well characterized.

Relaxation of Skeletal Muscles

Relaxation of Skeletal Muscles

The period of muscle contraction primarily influences the duration of stimulation at the neuromuscular junction (NMJ), the presence of free calcium ions in the sarcoplasm, and the availability of energy or ATP to support contractions.
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.

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Related Experiment Video

Updated: Jun 13, 2026

Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy

Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy

Published on: July 1, 2021

Pi release from myosin: a simulation analysis of possible pathways.

Marco Cecchini¹, Yuri Alexeev, Martin Karplus

¹Laboratoire de Chimie Biophysique, ISIS, Université de Strasbourg, 67000 Strasbourg, France. mcecchini@isis.u-strasbg.fr

Structure (London, England : 1993)

|April 20, 2010

Summary

Phosphate (Pi) release from myosin II is crucial for actomyosin function. Simulations reveal distinct pathways for Pi release in different myosin states, suggesting a mechanism for actin-activated acceleration.

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Last Updated: Jun 13, 2026

Dissecting Mechanoenzymatic Properties of Processive Myosins with Ultrafast Force-Clamp Spectroscopy

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Published on: July 1, 2021

Probing Myosin Ensemble Mechanics in Actin Filament Bundles Using Optical Tweezers

Probing Myosin Ensemble Mechanics in Actin Filament Bundles Using Optical Tweezers

Published on: May 4, 2022

Area of Science:

Biochemistry
Molecular Biology
Structural Biology

Background:

Phosphate (Pi) release is a key step in actomyosin motor function.
Actin binding accelerates Pi release, but the underlying structural mechanisms are not fully understood.

Purpose of the Study:

To elucidate the structural elements and pathways governing Pi release from myosin II.
To investigate how different myosin II structural states influence the rate of Pi release.

Main Methods:

Molecular dynamics simulations were employed to study slow processes like Pi release.
Analysis of isolated myosin II structures in various states (pre-powerstroke, post-rigor, rigor-like).
Mutant simulations were used to evaluate the role of identified residues in Pi release pathways.

Main Results:

Pi release is slow in the pre-powerstroke state, hindering premature power stroke.
Pi release is significantly faster in post-rigor and rigor-like states.
The 'backdoor' pathway is dominant in pre-powerstroke and post-rigor states, while a different pathway prevails in the rigor-like state.

Conclusions:

Distinct structural pathways dictate the rate of Pi release in different myosin II conformations.
These findings provide insights into the actin-activated acceleration of Pi release, a fundamental aspect of muscle contraction.