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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.

Microtubule Associated Motor Proteins

Microtubule Associated Motor Proteins

Eukaryotic cells have different motor proteins for transporting various cargo within the cell. These motor proteins differ based on the filament they associate with, the direction they move within the cell, and the type of cargo they transport. Motor proteins that associate with microtubules are known as microtubule-associated motor proteins. There are two families of microtubule-associated motor proteins —Kinesins and Dyneins. Both these proteins assist in the transport of cellular cargos...

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...

Role of Myosin in Cell Migration

Role of Myosin in Cell Migration

Myosins are multimeric motor proteins involved in various cellular processes such as migration, adhesion, and proliferation. Myosin II is the most common type in animal cells, which binds and cross-links actin filaments.
Myosin II is a hexamer comprising two heavy chains with globular heads and coiled-coil tails, two regulatory light chains, and two essential light chains. The ATPase sites on the myosin heads hydrolyze ATP, and the released phosphate generates the force for contraction. It is...

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 Movement of Organelles and Vesicles

The Movement of Organelles and Vesicles

In eukaryotic cells, cytoskeletal filaments such as actin, microtubules, and intermediate filaments form a mesh-like cytoskeletal network. These filaments serve as tracks for transporting cellular cargo. Specialized motor proteins use the chemical energy stored in adenosine triphosphate (ATP) for this transport. During interphase, microtubules are polarized, with the plus-end towards the cell periphery and the minus-end towards the cell center. Two microtubule-associated motor proteins,...

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Related Experiment Video

Updated: Jul 3, 2026

Myosin-Specific Adaptations of In vitro Fluorescence Microscopy-Based Motility Assays

Myosin-Specific Adaptations of In vitro Fluorescence Microscopy-Based Motility Assays

Published on: February 4, 2021

Dictyostelium myosin-5b is a conditional processive motor.

Manuel H Taft¹, Falk K Hartmann, Agrani Rump

¹Institute for Biophysical Chemistry, OE 4350, Hannover Medical School, Feodor-Lynen-Str. 5, D-30625 Hannover, Germany.

The Journal of Biological Chemistry

|July 25, 2008

Summary

Dictyostelium myosin-5b, a motor protein, shows altered movement with changes in magnesium ion concentration. This suggests a mechanism for switching between processive and non-processive movement in cells.

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Published on: July 1, 2021

Area of Science:

Molecular biology
Cell biology
Biochemistry

Background:

Dictyostelium myosin-5b (myoJ) is one of two related myosin-5 isoenzymes in Dictyostelium discoideum.
Myosin motors are crucial for cellular functions involving movement along actin filaments.

Purpose of the Study:

To investigate the kinetic and functional properties of Dictyostelium myosin-5b.
To understand how magnesium ion concentration affects myosin-5b activity and movement.

Main Methods:

Kinetic analysis of Dictyostelium myosin-5b.
Biochemical assays measuring ATPase activity and actin binding.
In vitro motility assays.

Main Results:

Dictyostelium myosin-5b exhibits high actin affinity, fast ATP hydrolysis, and high ATPase activity, characteristic of a processive motor.
Decreased free Mg(2+) concentration increases ADP release rate and reduces time in strong actin binding states.
Motor's ability to translocate actin filaments at low densities decreases with lower Mg(2+) concentrations.

Conclusions:

Physiological changes in Mg(2+) concentration impact Dictyostelium myosin-5b motor activity.
A mechanism is proposed for switching between processive and non-processive movement based on Mg(2+) levels.
These findings have implications for understanding molecular motor function in cellular processes.