InterPro domain: IPR001609

Muscle contraction is caused by sliding between the thick and thin filaments of the myofibril. Myosin is a major component of thick filaments and exists as a hexamer of 2 heavy chains [ 1 ], 2 alkali light chains, and 2 regulatory light chains. The heavy chain can be subdivided into the N-terminal globular head and the C-terminal coiled-coil rod-like tail, although some forms have a globular region in their C-terminal. There are many cell-specific isoforms of myosin heavy chains, coded for by a multi-gene family [ 2 ]. Myosin interacts with actin to convert chemical energy, in the form of ATP, to mechanical energy [ 3 ]. The 3-D structure of the head portion of myosin has been determined [ 4 ] and a model for actin-myosin complex has been constructed [ 5 ].

The globular head is well conserved, some highly-conserved regions possibly relating to functional and structural domains [ 6 ]. The rod-like tail starts with an invariant proline residue, and contains many repeats of a 28 residue region, interrupted at 4 regularly-spaced points known as skip residues. Although the sequence of the tail is not well conserved, the chemical character is, hydrophobic, charged and skip residues occuring in a highly ordered and repeated fashion [ 7 ].

1. The primary structure of skeletal muscle myosin heavy chain: I. Sequence of the amino-terminal 23 kDa fragment. J. Biochem. 110, 54-9
2. Human embryonic myosin heavy chain cDNA. Interspecies sequence conservation of the myosin rod, chromosomal locus and isoform specific transcription of the gene. FEBS Lett. 256, 21-8
3. Conserved protein domains in a myosin heavy chain gene from Dictyostelium discoideum. Proc. Natl. Acad. Sci. U.S.A. 83, 9433-7
4. Three-dimensional structure of myosin subfragment-1: a molecular motor. Science 261, 50-8
5. Structure of the actin-myosin complex and its implications for muscle contraction. Science 261, 58-65
6. Protein structural domains in the Caenorhabditis elegans unc-54 myosin heavy chain gene are not separated by introns. Proc. Natl. Acad. Sci. U.S.A. 80, 4253-7