myosins
Myosins are molecular motors that, upon interaction with actin filaments, utilize energy from ATP hydrolysis to generate mechanical force.
Phylogenetic analysis of the myosin motor domains identified 11 distinct classes, 7 of which are expressed in vertebrates.
These 7 vertebrate myosin classes include conventional myosin (myosin II) and 6 less well characterized unconventional myosin classes, myosins I, V (MIM.160777), VI (MIM.600970), VII (MIM.276903), IX, and X (MIM.601481).
Each myosin has a conserved N-terminal motor domain (25 to 40% identical at the amino acid level) that contains both ATP-binding and actin-binding sequences.
Following the motor domain is a light-chain-binding ’neck’ region containing 1-6 copies of a repeat element, the IQ motif, that serves as a binding site for calmodulin (MIM.114180) or other members of the EF-hand superfamily of calcium-binding proteins.
At the C terminus, each myosin class has a distinct tail domain that serves in dimerization, membrane binding, protein binding, and/or enzymatic activities and targets each myosin to its particular subcellular location.
Structure
In vertebrate striated muscle, myosin is composed of 2 heavy chains of about 200,000 daltons each (myosin heavy chains - MYHs) and 4 light chains of about 20,000 daltons each (mysoin light chains - MYLs).
Phylogenetic analysis of the myosin heavy chains motor domains identified 11 distinct classes, 7 of which are expressed in vertebrates. These 7 vertebrate myosin heavy chains classes include conventional myosin (myosin II) and 6 less well characterized unconventional myosin classes, myosins I, V, VI, VII, IX, and X.
Members
| myosin-I | MYO1A | MYO1B | MYO1C | MYO1D | MYO1E | MYO1F |
| myosin-II | MYO2 | |||||
| myosin-III | MYO3 | |||||
| myosin-IV | MYO4 | |||||
| myosin-V | MYO5A | MYO5B | ||||
| myosin-VI | MYO6 | |||||
| myosin-VII | MYO7A | MYO7B | ||||
| myosin-VIII | MYO8 | |||||
| myosin-IX | MYO9A | MYO9B |
Structure
Each myosin has a conserved N-terminal motor domain (25 to 40% identical at the amino acid level) that contains both ATP-binding and actin-binding sequences.
Following the motor domain is a light-chain-binding ’neck’ region containing 1-6 copies of a repeat element, the IQ motif, that serves as a binding site for calmodulin or other members of the EF-hand superfamily of calcium-binding proteins. At the C terminus, each myosin class has a distinct tail domain that serves in dimerization, membrane binding, protein binding, and/or enzymatic activities and targets each myosin to its particular subcellular location.
Pathology
| MYO1A | autosomal dominant nonsyndromic deafness | |
| MYO5A | Griscelli disease | |
| MYO6 | recessive deafness DFNB37 | |
| MYO7A | Usher syndrome type I | MIM.276903 |
| MYO9B | celiac disease susceptibility | MIM.609753 |
References
Matsumura F. Regulation of myosin II during cytokinesis in higher eukaryotes. Trends Cell Biol. 2005 May 31; PMID: 15935670
Karcher RL, Deacon SW, Gelfand VI. Motor-cargo interactions : the key to transport specificity. Trends Cell Biol. 2002 Jan ;12(1):21-7. PMID : 11854006
Rodriguez OC, Cheney RE. A new direction for myosin. Trends Cell Biol. 2000 Aug;10(8):307-11. PMID: 10884682
Mermall V, et al: Unconventional myosins in cell movement, membrane traffic and signal transduction. Science 279:527, 1998.
