Tropomyosin
Tropomyosinum
A long α-helical coiled-coil protein that lies in the grooves of F-actin. At rest it blocks the myosin-binding sites.
Overview
Tropomyosin dimers (≈40 nm long) join head-to-tail into a continuous strand along each groove of the actin double helix. Each molecule spans seven actin monomers and carries one troponin complex. At rest, troponin I holds tropomyosin in a "blocked" position over the myosin-binding sites. When Ca²⁺ binds troponin C, tropomyosin rolls azimuthally into the groove (the "closed" state). Strong myosin binding then pushes it further (the "open" state). This cooperative movement lets one Ca²⁺-binding event activate several neighbouring actin sites, which makes the force–Ca²⁺ relationship steep.
Function
- Sterically blocks cross-bridge formation at rest
- Spreads activation cooperatively along the thin filament
- Stabilises F-actin
Clinical significance
Tropomyosin myopathies
Mutations in the TPM2 and TPM3 genes cause nemaline and cap myopathies. TPM1 mutations cause familial hypertrophic cardiomyopathy.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.