Myosin
Motor proteins driving actin-based motility and muscle contraction.
Myosins are a family of motor proteins, often protein complexes, best known for their roles in muscle contraction and a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-based motility.
- discovered_by
- Wilhelm Kühne
- type
- Family of motor proteins
- function
- Actin-based motility, muscle contraction
- key_properties
- ATP hydrolysis, actin binding, force transduction
- known_for
- Muscle contraction and cellular motility
Lore & Background
The term was later extended to include a group of similar ATPases found in both striated and smooth muscle tissue.
Reader's Guide
Myosins are a large superfamily of genes whose protein products share the basic properties of actin binding, ATP hydrolysis, and force transduction. Virtually all eukaryotic cells contain myosin isoforms, with some specialized in muscle cells and others ubiquitous. The structure and function of myosin is globally conserved across species, to the extent that rabbit muscle myosin II will bind to actin from an amoeba. The wide variety of myosin genes found throughout eukaryotic phyla were named according to different schemes, leading to some confusion in nomenclature. Skeletal muscle myosin, the most conspicuous, was the first discovered and forms part of the sarcomere. Beginning in the 1970s, researchers discovered new myosin genes in simple eukaryotes encoding monomeric proteins, termed Class I myosins or 'unconventional myosins,' found in many tissues other than muscle. These are grouped according to phylogenetic relationships of their head domains, with each class assigned a Roman numeral. The diverse array of myosins likely evolved from an ancestral precursor. Analysis shows great variability among tail domains but strong conservation of head domain sequences, allowing myosins to interact with different cargoes while maintaining the same motor machinery. The human genome contains over 40 different myosin genes.
Did You Know?
- Myosin II is responsible for muscle contraction and is also found in non-muscle cells in contractile bundles called stress fibers.
- Myosin VI is the only myosin that moves toward the pointed (-) end of actin filaments.
- The human genome contains over 40 different myosin genes.
Frequently Asked Questions
What are Myosin's powers or role?
Myosin converts the chemical energy released by ATP hydrolysis into mechanical force, pulling along actin filaments to drive muscle contraction and a wide range of other motility processes. Its core toolkit includes actin binding, force transduction, and an ATP-dependent power stroke.
How does Myosin's cycle work?
In each round, myosin attaches to actin, hydrolyzes ATP to trigger a conformational change that produces a power stroke, then detaches and re-cocks for the next cycle. This repetitive mechanochemical loop is what sustains both sustained contraction and directional cellular movement.
Why is Myosin important?
Without myosin, eukaryotic cells would lose their primary engine for actin-based motility, and striated muscle could not generate contraction. It underpins everything from heartbeat and locomotion to cytokinesis and intracellular cargo transport.
How is Myosin different from other motor proteins?
While kinesin and dynein walk along the microtubule network, myosins are the dedicated engines of the actin cytoskeleton. This track specialization gives cells a second, distinct system for generating force and movement.
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