Myosin

Part of the myosin II structure

A myosin is a group of specialized proteins used for muscle contraction and motion in eukaryotic cells. Myosins need adenosine triphosphate for energy to do these functions. A large number of different myosin genes have been discovered in eukaryotes.

The structure and function of myosin is strongly conserved across species. For example, Rabbit muscle myosin II will bind to actin from an amoeba.^[1]

Structure and function

Parts

Most myosin molecules are composed of a head part, a neck part, and a tail part.

The head part grabs onto the actin, and uses energy from ATP to pull, making the muscle shorter.
the neck part acts as a lever.
The tail part mostly interacts with other molecules or other myosin subunits. In some cases, the tail part may help regulate movement.

Power stroke

Many myosin molecules can make muscles get shorter using the energy released from breaking apart ATP molecules into ADP molecules and a phosphate group.^[2] The power stroke happens when a phosphate that n broken off gets released from the myosin. This makes the myosin change shape so that it pulls against the actin. When the ADP molecule is released and a new ATP molecule joins onto the myosin head, the head releases from the actin. The myosin breaks the new ATP and the cycle keeps going. The combined effect of all the power strokes from all the different myosin molecules makes the muscle get shorter.

Myosin Media

Myosin unrooted phylogenetic tree
Sliding filament model of muscle contraction.
Cardiac sarcomere structure featuring myosin
Crystal structure of myosin V motor with essential light chain – nucleotide-free
A ribbon diagram of the Myosin V molecular motor pseudo-colored to illustrate major subdomains. In the interest of visual clarity, important loops (which are often labeled separately in the literature) are not singled out. This perspective highlights the nucleotide-binding site and the separation of the U50 and L50 subdomains which form the actin-binding site cleft.
State of myosin VI from PDB 2V26 before the power stroke

References

↑ McMahon, T. A. 1984. Muscles, reflexes and locomotion'. Princeton University Press. ISBN 978-0-691-02376-2
↑ Tyska, Matthew J.; Warshaw, David M. (2002). "The myosin power stroke". Cell Motility and the Cytoskeleton. 51 (1): 1–15. doi:10.1002/cm.10014. PMID 11810692.

[McMahon-1] McMahon, T. A. 1984. Muscles, reflexes and locomotion'. Princeton University Press. ISBN 978-0-691-02376-2

[2] Tyska, Matthew J.; Warshaw, David M. (2002). "The myosin power stroke". Cell Motility and the Cytoskeleton. 51 (1): 1–15. doi:10.1002/cm.10014. PMID 11810692.

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