User:ListeningLearner29/Myosin

Self-inhibition of Myosin II [1][2][4]. The movie begins with Myosin II in the 10S conformation with a folded tail domain, the blocked head and free head [2][3]. The movie schematically depicts tail unfolding and the resulting active 6S confirmation [2][3] followed by tail folding back to the 10S conformation. The illustration is conceptual: transitory states and diffusive motions associated with folding/unfolding are not shown [4].

Article Draft

Article body

Myosin II[edit]

Myosin II (also known as conventional myosin) is the myosin type responsible for producing muscle contraction in muscle cells in most animal cell types. It is also found in non-muscle cells in contractile bundles called stress fibers.

• Myosin II contains two heavy chains, each about 2000 amino acids in length, which constitute the head and tail domains. Each of these heavy chains contains the N-terminal head domain, while the C-terminal tails take on a coiled-coil morphology, holding the two heavy chains together (imagine two snakes wrapped around each other, as in a caduceus). Thus, myosin II has two heads. The intermediate neck domain is the region creating the angle between the head and tail. In smooth muscle, a single gene (MYH11)) codes for the heavy chains myosin II, but splice variants of this gene result in four distinct isoforms.
• It also contains 4 myosin light chains (MLC), resulting in 2 per head, weighing 20 (MLC₂₀) and 17 (MLC₁₇) kDa. These bind the heavy chains in the "neck" region between the head and tail.
  • The MLC₂₀ is also known as the regulatory light chain and actively participates in muscle contraction.
  • The MLC₁₇ is also known as the essential light chain. Its exact function is unclear, but is believed to contribute to the structural stability of the myosin head along with MLC₂₀. Two variants of MLC₁₇ (MLC_17a/b) exist as a result of alternative splicing at the MLC₁₇ gene.

In muscle cells, the long coiled-coil tails of the individual myosin molecules can auto-inhibit active function in the 10S conformation or upon phosphorylation, change to the 6S conformation and join, forming the thick filaments of the sarcomere. [3][4] The force-producing head domains stick out from the side of the thick filament, ready to walk along the adjacent actin-based thin filaments in response to the proper chemical signals and may be in either auto-inhibited or active conformation. The balance/transition between active and inactive states is subject to extensive chemical regulation.

Further information: Muscle contraction

Further information: Meromyosin