Skeletal muscle fiber proteins

actin

a contractile protein that is the main component of the thin filament. On each actin molecule is a myosin-binding site where a myosin head of a thick filament bind during muscle contraction

tropomyosin

a regulatory protein that is a component of the thin filament. When a skeletal muscle fiber is relaxed, it covers the myosin -binding sites on actin molecules, thereby preventing myosin from binding to actin

troponin

a regulatory protein that is a component of the thin filament. When calcium ions (Ca2+) bind to it, 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.

a-actinin

a structural protein of the Z discs that attaches to actin molecules of thin filaments and to titin molecules

titin

a structural protein that connects a Z disc to the M line of the sarcomere, thereby helping to stabilize the positions of the thick filament. Because it can stretch and then spring back unharmed, it accounts for much of the elasticity and extensibility of myofibrils

myomesin

a structural protein that forms the M line of the sarcomere; it binds to titin molecules and connects adjacent thick filaments to one another

dystrophin

a structural protein that links the thin filaments of the sarcomere to intergral membrane proteins in the sarcolemma, which are attached in turn to proteins in the connective tissue matrix that surrounds muscle fibers. it is thought that it helps reinforce the sarcolemma and that it helps transmit tension generated by sarcomeres to tendons.

nebulin

a structural protein that wraps around the entire length of each thin filament; it helps anchor the thin filaments to the Z disc and regulates the length of the thin filaments during development

contractile proteins

proteins that generate force during muscle contractions

regulatory proteins

proteins that help switch the muscle contraction process on and off

Structural proteins

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

myosin

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