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myosins

Monday 15 September 2003

Myosins are proteic motors. Upon interaction with actin filaments, they utilize energy from ATP hydrolysis to generate mechanical force.

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.