Proteins found in the muscle

Actin

Contractile protein that is the main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction

Myosin

Contractile protein that makes up the thick filament; molecule consists of a tail and two myosin heads, which bind to myosin-binding sites on actin molecules of thin filament during muscle contraction

Tropomyosin

Regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin

Dystrophin

Structural protein that links thin filaments of sarcomere to integral membrane proteins in sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers; thought to help reinforce sarcolemma and help transmit tension generated by sarcomeres to tendons

Nebulin

Structural protein that wraps around entire length of each thin filament; helps anchor thin filaments to Z discs and regulates length of thin filaments during development

Troponin

a regulatory protein that is a component of the thin filament. When calcium ions (Ca2+) bind to troponin, it undergoes a change in shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin

Regulatory proteins

proteins that help switch muscle contraction process on and off

structual proteins

proteins that keep thick and thin filaments of myofibrils in proper alignment, give myofibrils elasticity and extensibility, and link myofibrils to sarcolemma and extracellular matrix

contractile proteins

Proteins that generate force during muscle contractions

Titin

Structural protein that connects Z disc to M line of sarcomere, thereby helping to stabilize thick filament position; can stretch and then spring back unharmed, and thus accounts for much of the elasticity and extensibility of myofibrils.

Myomesin

Structural protein that forms M line of sarcomere; binds to titin molecules and connects adjacent thick filaments to one another

a- actin

Structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules