betamyosin

Betamyosin, often referred to as beta-myosin heavy chain (β-MHC), is a motor protein in cardiac and skeletal muscle belonging to the myosin II family. It forms part of the thick filament of the contractile apparatus and uses energy from ATP hydrolysis to move along actin filaments, generating force and sarcomere shortening.

The β-MHC heavy chain is encoded by the MYH7 gene in humans. In adult human ventricles it is the predominant cardiac myosin heavy chain; another cardiac isoform, α-myosin heavy chain (MYH6), is more prevalent in atria and fetal or rodent hearts. Expression shifts during development and in disease.

Structure: the protein is a ~220–250 kDa heavy chain with an N-terminal motor domain (head) containing ATPase activity and actin-binding sites, a neck region with regulatory and essential light chains, and a long coiled-coil tail that mediates dimerization and thick-filament assembly in the sarcomere.

Function: β-MHC acts as the motor component of the thick filament, converting chemical energy from ATP into mechanical work by moving along actin during the contractile cycle. Its slower ATPase activity relative to other myosin II isoforms confers slower cross-bridge cycling and contraction velocity, which supports sustained force generation in cardiac muscle.

Regulation and clinical aspects: expression and activity are influenced by developmental cues, thyroid state, and metabolic conditions; regulatory light-chain phosphorylation modulates performance. Mutations in MYH7 are a common cause of inherited cardiomyopathies, including hypertrophic and dilated cardiomyopathy, and are targets of diagnostic and therapeutic research.

See also: myosin II, MYH7, hypertrophic cardiomyopathy.