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myosin heavy chains

Saturday 13 March 2004

Myosin heavy chains (MYHs) are ubiquitous actin-based motor proteins that convert the chemical energy derived from hydrolysis of ATP into mechanical force that drives diverse motile processes, including cytokinesis, vesicular transport, and cellular locomotion, in eukaryotic cells.

In mammals at least 10 different myosin heavy chain (MHC) isoforms have been described from striated, smooth, and nonmuscle cells. These isoforms show expression that is spatially and temporally regulated during development. The hexameric myosin molecule consists of 2 heavy chains (200 kD each) and 2 pairs of light chains (16 to 20 kD each). The heavy chain can be divided into 2 domains, the globular amino terminal head responsible for binding to the myosin light chain and to actin as well as for ATP hydrolysis, and the alpha-helical carboxy terminal rod responsible for the ability of myosin to form filaments.

The MYHCs have been divided into 9 to 11 classes. The structural gene for the beta heavy chain of myosin is expressed predominantly in fetal life and is switched on in older animals under conditions of thyroid hormone depletion/replacement and in response to some physical stresses. Embryonic MYH3 (MIM.160720) and perinatal MYHCs predominate early during skeletal muscle development, persist in certain specialized muscles, such as extraocular and masseter, and are reexpressed in regenerating muscles.

Class II, or ’conventional,’ MYHCs include the extensively studied group of sarcomeric MYHCs that self associate to form filaments and function enzymatically to promote contraction in striated (cardiac and skeletal) muscles.


Muscle myosin is a heterohexamer consisting of 2 myosin heavy chains and 2 associated nonidentical pairs of myosin light chains. The 7 MYHC isoforms that predominate in mammalian skeletal muscles include 2 developmental isoforms, MYHC-embryonic (MYH3)(MIM.160720) and MYHC-perinatal (MYH8)(MIM.160741); 3 adult skeletal muscle isoforms, MYHC-IIa (MYH2) (MIM.160740), MYHC-IIb (MYH4) (MIM.160742), MYHC-IIx/d (MYH1); and MYHC-beta/slow (MYH7) (MIM.160760), which is also expressed in cardiac muscle. MYHC-extraocular (MYH13) (MIM.603487) is expressed primarily in extrinsic eye muscles.




Gene mutations in OMIM
MYH2 inclusion body myopathy-3 (IBM3) MIM.605637
MYH6 familial hypertrophic cardiomyopathy MIM.192600
MYH7 familial hypertrophic cardiomyopathy MIM.192600
MYH9 May-Hegglin anomaly MIM.155100
MYH9 Sebastian syndrome MIM.605249
MYH9 Fechtner syndrome MIM.153640
MYH9 autosomal dominant deafness (DFNA17) MIM.603622
MYH9 Alport-like syndrome with macrothrombocytopenia (Epstein syndrome) MIM.153650
MYH11 CBFB/MYH11 fusion protein in acute myeloid leukemia
MYH12 Griscelli disease (MYO5A) MIM.214450
MYH14 autosomal dominant hearing impairment (DFNA4)