Fast skeletal muscle myosin (None commonly used; sometimes abbreviated as "fast MyHC" (myosin heavy chain) in literature, but no universal abbreviation.)

Fast skeletal muscle myosin refers to a family of motor proteins predominantly expressed in **fast-twitch** fibers (**type II fibers**) within vertebrate **skeletal muscles**. These proteins are responsible for rapid contractions required during activities such as sprinting or sudden movements. Structurally, each molecule consists primarily of two heavy chains—encoded by genes such as *MYH1*, *MYH2*, *MYH4*—and four light chains. The head domain binds actin filaments and hydrolyzes ATP to generate mechanical force through conformational changes known as power strokes[5][7]. This process underlies the sliding filament mechanism central to all striated muscular contraction. Fast-type isoforms differ from their slow counterparts by exhibiting higher ATPase activity and faster crossbridge cycling rates, enabling quick but less fatigue-resistant contractions compared to slow-twitch fibers[4]. In addition to their primary role in movement generation, alterations or mutations affecting these molecules—or their regulatory partners like **fast skeletal myosin-binding protein-C** (*fMyBP-C*)—are implicated in various inherited muscular diseases including distal arthrogryposis and other forms of congenital weakness syndromes[1][3]. Therapeutic interest centers on modulating these proteins' function either directly through small molecules that affect contractility kinetics or indirectly via pathways regulating calcium sensitivity. However, achieving tissue-specific effects without impacting cardiac function remains an ongoing challenge due to structural similarities among different striated-muscle isoforms.

Other names

Fast myosinType II myosinSkeletal muscle type II myosin heavy chain (MyHC-II)Myh1, Myh2, Myh4 (gene/protein isoforms for human fast skeletal muscle)Fast-twitch myosin

For drugs targeting this molecule or its pathway— – Modulation of actin-myosin interaction kinetics to enhance force production or slow relaxation. – Alteration of calcium sensitivity within the contractile apparatus. – Stabilization or destabilization of crossbridge formation between actin and fast-type myosins.