Tropomyosin

Tropomyosin is a type of protein that plays a crucial role in muscle contraction. It is a component of the thin filament, which is part of the contractile apparatus in muscle cells. Tropomyosin, along with troponin, regulates the interaction between actin and myosin, the two main proteins involved in muscle contraction.

Structure

Tropomyosin is a coiled-coil protein that wraps around the actin filament in muscle cells. It is made up of two alpha-helical chains that are wound around each other, forming a long, thin, flexible rod. Each tropomyosin molecule spans seven actin monomers, and the tropomyosin molecules align end-to-end along the length of the actin filament.

Function

The primary function of tropomyosin is to regulate muscle contraction. It does this by blocking the binding sites on actin for myosin, preventing the myosin heads from attaching to the actin filament and initiating contraction. When a muscle cell is stimulated to contract, calcium ions bind to troponin, causing a conformational change in the troponin-tropomyosin complex that moves tropomyosin away from the myosin-binding sites on actin. This allows myosin to bind to actin and initiate muscle contraction.

Role in disease

Mutations in the genes that encode tropomyosin can lead to various types of myopathy, a group of diseases that affect muscle function. For example, mutations in the TPM2 and TPM3 genes, which encode beta-tropomyosin and gamma-tropomyosin respectively, can cause nemaline myopathy, a rare genetic disorder characterized by muscle weakness and the presence of rod-like structures called nemaline bodies in muscle cells.

See also

• Actin
• Myosin
• Troponin
• Muscle contraction
• Myopathy
• Nemaline myopathy

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