What is the function of actin

Actin

Synonyms: actin, thin filament, I-filament
English: actin, actin, thin filament

1 definition

Under the globular Actin one understands a structural protein that can be found in the cytoskeleton and in the sarcomere of the muscle fiber. Here, together with myosin, troponin and tropomyosin, it forms the contractile unit of the muscle. Actin occurs in almost all eukaryotic cells and has a conserved structure.

2 classification

Different isoforms (depending on the charge) of actin can be distinguished:

  • α-actin
  • β-actin
  • γ-actin

However, there are also an α-cardiac muscle, an α- and a γ-smooth muscle, as well as a β- and a γ-non-muscle actin.

3 structure

The actin found in skeletal muscle is α-actin. It has a molecular mass of approx. 42 kDa (approx. 375 amino acids) and a diameter of approx. 4-8 nm. An actin molecule alone is referred to as G-actin. It exists as a so-called monomer. Several of these actin monomers form the filamentous one with the consumption of ATP F-actin. Two of these F-actin strands form microfilaments that are in a double-helical structure. Actin is a dynamic molecule and can therefore be built up and broken down quickly.

Tropomyosin threads are woven around the actin molecules, and every 7 actin molecules are followed by three horizontally lying troponin peptides. Nebulin spirals around the actin filament and thereby stabilizes it. Together with actinin, it anchors actin on the Z-disks.

4 function

Actin plays a crucial role in muscle contraction in particular. Its interaction with the myosin is a basis for muscle contraction (sliding filament theory).