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 [ PUBMED:1939027 ], 2 alkali light chains, and 2 regulatory light chains. The heavy chain can be subdivided into the N-terminal globular … expand

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 [ PUBMED:1939027 ], 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 [ PUBMED:2806546 ]. Myosin interacts with actin to convert chemical energy, in the form of ATP, to mechanical energy [ PUBMED:3540939 ]. The 3-D structure of the head portion of myosin has been determined [ PUBMED:8316857 ] and a model for actin-myosin complex has been constructed [ PUBMED:8316858 ].

The globular head is well conserved, some highly-conserved regions possibly relating to functional and structural domains [ PUBMED:6576334 ]. 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 [ PUBMED:6576334 ].

This domain is also found in chitinases present in filamentous fungi, enzymes that play a critical role in promoting the synthesis of chitin at the hyphal tip, thus influencing fungal growth and the architecture of fungal infection structures [ PUBMED:31681248 PUBMED:22964252 ].