Structure of the thin filament and Z-line

Items covered in this animation:

• Actin (thin filaments). These are only described briefly, but more is focused on the accessory proteins that accompany actin in the thin filament
• Capping proteins, specialised molecules which bind to the ends of the actin filaments, preventing them from either elongating or shrinking. The example of CapZ is shown in the animation, with another possible capping protein being tropomodulin.
• Nebulin, a non-elastic structural protein that stretches the entire length of the thin filament in skeletal muscle.
• The position and structure of the regulatory complex (Tropomyosin and the Troponin complex) is briefly described.
• a-Actinin, a 102 kDa protein which is found in the z-disks and is known to make strong complexes with F-actin. This is, in-turn bound to another z-disk polypeptide Myotilin.
• Titin, a massive 3 MDa protein which stretches an entire half sarcomere and helps maintain the position of the thick filaments. In the Z-disks this has an enzymic activity as well as it can phosphorylate a protein called Telethonin.
• Desmin, a member of a class of fibrous proteins called 'intermediate filaments'. Desmin surrouns the outside of the Z-disks and allows then to be link to both the sarcolemma and to neighbouring sarcomere's via further binding proteins.