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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...

Actin Polymerization and Cell Motility

Actin Polymerization and Cell Motility

Actin is a family of globular proteins that are highly abundant in eukaryotic cells. It makes up approximately 1-5% of total cell protein concentration. Actin monomers polymerize to form a complex network of polarized filaments, the actin cytoskeleton, that plays a crucial role in many cellular processes, including cell motility, division, endocytosis, and metastasis of cancer cells.
Actin cytoskeleton dynamics can produce pushing, pulling, and resistance forces that help the cell to migrate.

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...

The Sarcomere

The Sarcomere

A sarcomere is a microscopic segment repeating in a myofibril. The sarcomere fundamentally consists of two main myofilaments: thick filaments called myosin and thin filaments called actin. These filaments interact by sliding past each other in response to stimulus. In addition to myosin and actin, several other proteins, such as tropomyosin, troponin, titin, nebulin, myomesin, α-actinin, and dystrophin, play crucial roles in regulating, structuring, and functioning of the sarcomere.
Each myosin...

Introduction to Actin

Introduction to Actin

Actin is a highly conserved cytoskeletal protein found abundantly in eukaryotic cells. It constitutes 10% weight of the total cellular protein in muscle cells, while in non-muscle cells, it is lower and makes up around 1–5 percent of the total cell protein. Actin found in the unicellular amoebae and complex multicellular animals is around 80% similar, demonstrating their conservation over a billion years of evolution. Actin coding genes are conserved within species and across different species.

Muscle Contraction

Muscle Contraction

In skeletal muscles, acetylcholine is released by nerve terminals at the motor endplate—the point of synaptic communication between motor neurons and muscle fibers. The binding of acetylcholine to its receptors on the sarcolemma allows entry of sodium ions into the cell and triggers an action potential in the muscle cell. Thus, electrical signals from the brain are transmitted to the muscle. Subsequently, the enzyme acetylcholinesterase breaks down acetylcholine to prevent excessive muscle...

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Updated: May 24, 2026

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Published on: July 30, 2014

A myopathy-related actin mutation increases contractile function.

Johan Lindqvist¹, Isabelle Pénisson-Besnier, Hiroyuki Iwamoto

¹Department of Neuroscience, Clinical Neurophysiology, Uppsala University, Sweden.

Acta Neuropathologica

|February 24, 2012

Summary

Nemaline myopathy, caused by ACTA1 gene mutations, affects muscle contraction. This study reveals how a specific actin mutation enhances muscle force despite altering cross-bridge dynamics.

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Myo-mechanical Analysis of Isolated Skeletal Muscle

Myo-mechanical Analysis of Isolated Skeletal Muscle

Published on: February 22, 2011

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Last Updated: May 24, 2026

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Aip1p Dynamics Are Altered by the R256H Mutation in Actin

Published on: July 30, 2014

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

Myo-mechanical Analysis of Isolated Skeletal Muscle

Myo-mechanical Analysis of Isolated Skeletal Muscle

Published on: February 22, 2011

Area of Science:

Muscle physiology and biophysics
Molecular genetics and cell biology
Biochemistry and structural biology

Background:

Nemaline myopathy (NM) is the most common congenital myopathy, often linked to mutations in genes like ACTA1, which encodes skeletal alpha-actin.
ACTA1 mutations, typically causing single amino acid substitutions in actin, have poorly understood effects on muscle contractility.
Understanding these subtle changes is crucial for developing targeted therapies for NM patients.

Observation:

This study investigated the mechanical and structural consequences of a specific actin mutation (p.Phe352Ser) in human muscle fibers using X-ray diffraction and mechanical recordings.
The p.Phe352Ser substitution was found to significantly increase the strain experienced by individual actin-myosin cross-bridges during muscle contraction.
Paradoxically, this mutation also reduced the number of attached cross-bridges by affecting myosin head attachment rates to actin.

Findings:

The p.Phe352Ser mutation triggers a complex molecular cascade impacting muscle fiber mechanics.
Despite reducing cross-bridge numbers, the enhanced strain per cross-bridge leads to improved steady-state force production at the cellular level.
These findings reveal a novel mechanism by which actin mutations influence muscle force generation.

Implications:

Provides critical insights into the structure-function relationship of actin in muscle contraction.
Offers a deeper understanding of the molecular basis of nemaline myopathy caused by ACTA1 mutations.
Informs the development of future therapeutic strategies aimed at correcting or mitigating the effects of actin defects in congenital myopathies.