Part of the myosin structure, atoms in the heavy chain are colored red on the left-hand side, and atoms in the light chains are colored orange and yellow.

Myosins are a large family of motor proteins found in eukaryotic tissues. Motor proteins are a class of Molecular motors that are able to move along the surface of a suitable substrate Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Tissue is a cellular organizational level intermediate between cells and a complete organism They are responsible for actin-based motility. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of Motility is a biological term which refers to the ability to move spontaneously and actively consuming energy in the process

Structure and Function

Sliding filament model of muscle contraction.

Domains

Most myosin molecules are composed of both a head and a tail domain.

• The head domain binds the filamentous actin, and uses ATP hydrolysis to generate force and to "walk" along the filament towards the (+) end (with the exception of one family member, myosin VI, which moves towards the (-) end). Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions

• The tail domain generally mediates interaction with cargo molecules and/or other myosin subunits. In Structural biology, a protein subunit or subunit protein is a single Protein Molecule that assembles (or " coassembles "

Myosin I

Myosin I's function is unknown, but it is believed to be responsible for vesicle transport or the contraction vacuole of cells. ^[1]

Myosin II

Myosin II is perhaps the best-studied example of these properties.

• Myosin II contains two heavy chains, each about 2000 amino acids in length, which constitute the head and tail domains. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Each of these heavy chains contains the N-terminal head domain, while the C-terminal tails take on a coiled-coil morphology, holding the two heavy chains together (imagine two snakes wrapped around each other, such as in a caduceus). The N-terminus (also known as the amino-terminus, NH2-terminus, N-terminal end or The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal end, or For the coiled coil shape in general see Coil. A coiled coil is a Structural motif in Proteins in which 2-7 The caduceus (/kəˈdjuːsiəs/ -ʃəs -ˈduː- κηρύκειον in Greek) or wand of Hermes is typically depicted as a short herald's staff Thus, myosin II has two heads.

• It also contains 4 light chains (2 per head), which bind the heavy chains in the "neck" region between the head and tail.

In muscle cells, it is myosin II that is responsible for producing the contractile force. Here, the long coiled-coil tails of the individual myosin molecules join together, forming the thick filaments of the sarcomere. For the coiled coil shape in general see Coil. A coiled coil is a Structural motif in Proteins in which 2-7 "A-band" redirects here For other uses of the term see A band. The force-producing head domains stick out from the side of the thick filament, ready to walk along the adjacent actin-based thin filaments in response to the proper chemical signals.

Evolution and family tree

Myosin unrooted phylogenetic tree — click on image to see larger version (Source: http://www.mrc-lmb.cam.ac.uk/myosin/trees/trees.html)

Myosin II, the most conspicuous of the myosin superfamily due to its abundance in muscle fibers, was the first to be discovered. A phylogenetic tree, also called an evolutionary tree, is a tree showing the Evolutionary relationships among various biological Species or other Skeletal muscle is a type of Striated muscle, which usually attaches to tendons However, beginning in the 1970s researchers began to discover new myosin variants, with one head (as opposed to myosin II's two) and largely divergent tail domains. These new superfamily members have been grouped according to their structural similarities, with each subfamily being assigned a Roman numeral. Roman numerals are a Numeral system originating in ancient Rome, adapted from Etruscan numerals. The now diverse array of myosins has evolved from an ancestral precursor (see picture).

Analysis of the amino acid sequences of different myosins shows great variability among the tail domains but almost perfect retention of the same head sequence. Presumably this is so the myosins may interact, via their tails, with a large number of different cargoes, while the goal in each case - to move along actin filaments - remains the same and therefore requires the same machinery in the motor. For example, the human genome contains over 40 different myosin genes. The human genome is the Genome of Homo sapiens, which is stored on 23 chromosome pairs History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance

These differences in shape also determine the speed at which myosins can move along actin filaments. The hydrolysis of ATP and the subsequent release of the phosphate group causes the "power stroke," in which the "lever arm" or "neck" region of the heavy chain is dragged forward. A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. Since the power stroke always moves the lever arm by the same angle, the length of the lever arm determines how fast the cargo will move. A longer lever arm will cause the cargo to traverse a greater distance even though the lever arm undergoes the same angular displacement - just as a person with longer legs can move farther with each individual step. Myosin V, for example, has a much longer neck region than myosin II, and therefore moves 30-40 nanometers with each stroke as opposed to only 5-10.

Genes in humans

Note that not all of these genes are active.

• Family I: MYO1A, MYO1B, MYO1C, MYO1D, MYO1E, MYO1F, MYO1G, MYO1H
• Family III: MYO3A, MYO3B
• Family V: MYO5A, MYO5B, MYO5C
• Family VI: MYO6
• Family VII: MYO7A, MYO7B
• Family IX: MYO9A, MYO9B, MYO10
• Family XV: MYO15A
• Family XVIII: MYO18A, MYO18B
• Heavy chain: MYH1, MYH2, MYH3, MYH4, MYH6, MYH7, MYH7B, MYH8, MYH9, MYH10, MYH11, MYH13, MYH14, MYH15, MYH16. Myosin IA, also known as Brush-border myosin-1 and MYO1A, is a human Gene. Myosin IB, also known as MYO1B, is a human Gene. Myosin IC, also known as MYO1C, is a human Gene. Myosin IE, also known as MYO1E, is a human Gene. Myosin IF, also known as MYO1F, is a human Gene. Myosin IIIA, also known as MYO3A, is a human Gene. Myosin VA (heavy chain 12 myoxin, also known as MYO5A, is a human Gene. Myosin VB, also known as MYO5B, is a human Gene. Myosin VI, also known as MYO6, is a Protein. It has been found in humans mice fruit flies (Drosophila melanogaster and nematodes (C Elegans Myosin VIIA (MYO7A is a member of the unconventional Myosin superfamily of Proteins. Myosin IXB, also known as MYO9B, is a human Gene. Myosin X, also known as MYO10, is a human Gene. Myosin XVA, also known as MYO15A, is a human Gene. Myosin XVIIIA, also known as MYO18A, is a human Gene. Myosin XVIIIB, also known as MYO18B, is a human Gene. Myosin heavy chain 1 skeletal muscle adult, also known as MYH1, is a human Gene. Myosin heavy chain 2 skeletal muscle adult, also known as MYH2, is a human Gene. Myosin heavy chain 3 skeletal muscle embryonic, also known as MYH3, is a human Gene. Myosin heavy chain 6 cardiac muscle alpha (cardiomyopathy hypertrophic 1, also known as MYH6, is a human Gene. MYH7 is a Gene encoding a Myosin heavy chain beta (MHC-β isoform (slow twitch expressed primarily in the heart Myosin heavy chain 8 skeletal muscle perinatal, also known as MYH8, is a human Gene. Myosin heavy chain 9 non-muscle, also known as MYH9, is a human Gene. Myosin heavy chain 10 non-muscle, also known as MYH10, is a human Gene. Myosin heavy chain 11 smooth muscle, also known as MYH11, is a human Gene. Myosin heavy chain 14, also known as MYH14, is a human Gene. The MYH16 gene encodes a protein called Myosin heavy chain 16 which is a muscle protein in mammals
• Light chain: MYL1, MYL2, MYL3, MYL4, MYL5, MYL6, MYL6B, MYL7, MYL9, MYLIP, MYLK, MYLK2, MYLL1

References

1. ^ Sutherland Macive (6/4/03). Myosin light chain 1 alkali skeletal fast, also known as MYL1, is a human Gene. Myosin light chain 2 regulatory cardiac slow, also known as MYL2, is a human Gene. Myosin light chain 3 alkali ventricular skeletal slow, also known as MYL3, is a human Gene. Myosin light chain 4 alkali atrial embryonic, also known as MYL4, is a human Gene. Myosin light chain 6 alkali smooth muscle and non-muscle, also known as MYL6, is a human Gene. Myosin light chain 6B alkali smooth muscle and non-muscle, also known as MYL6B, is a human Gene. Myosin light chain 7 regulatory, also known as MYL7, is a human Gene. MYL9 is a gene which codes a light chain of Myosin. Myosin regulatory light chain interacting protein, also known as MYLIP, is a human Gene. Myosin light chain kinase, also known as MYLK, is a human Gene. Myosin I. Retrieved on 2007-05-23. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne

• T. Hodge and M. J. T. V. Cope (2000). "A Myosin Family Tree". Journal of Cell Science 113: 3353-3354.   Entrez PubMed 10984423
• Molecular Biology of the Cell. The Entrez Global Query Cross-Database Search System is a powerful Federated search engine or Web portal that allows users to search many discrete Health sciences Alberts, Johnson, Lewis, Raff, Roberts, and Walter. 4th Edition. 949-952.

External links

Additional images

Phase 1	Phase 2	Phase 3	Phase 4
Myosin-painting	Myosin powerstroke

See also

• Motor protein
• Actin

External links

• Myosin Video A video of a moving myosin motor protein. Motor proteins are a class of Molecular motors that are able to move along the surface of a suitable substrate Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of
• MeSH Myosins
• The Myosin Homepage
• EC 3.6.4.1