Question

Do motor proteins undergo conformational changes when the motor travels?

Answer 1

Motor proteins are the proteins that help in muscle contraction and also responsible for the active transport of proteins and vesicles in cytoplasm.

They include myosin, kinesins etc travel along the cytoskeletal filaments by force dependent mechanism using the hydrolysis of ATP molecules which is associated with the nucleotide hydrolysis and convert into mechanical motion.

These undergo mechanochemical cycle of cytoskeletal filament binding results in conformational change and release of filaments

Muscle contraction starts when electric impulse travels down a motor neuron's axon to its motor end plates that triggers the release of acetylcholine that migrates to the receptors on the myofiber and results in depolarisation in sarcolemma.

Depolarization travels deep into the muscle activating calcium ions to release from the sarcoplasmic reticulum. This calcium binding to troponin results in the conformation change in the tropomyosin that opens the actin site and make cross bridge with the myosin this leads to the conformational change that pulls the actin filament in nucleotide state that slide past the myosin towards the center of sarcomere.

This stage is known as rigor state. Cross bridge is at 45^o angle relative to the filament . ATP binds to the actin head domain. The intrinsic activity of ATPase enzyme triggers the release of ADP and inorganic phosphate, where both of these bind to the myosin.

ATP hydrolysis activates the conformational change in the lever arm and myosin swings and binds to the new actin molecule where now cross bridge is 90⁰ angle relative to the filament.

The release of inorganic phosphate allows another conformational change and relaxation of lever arm back to its original state. This is known as power stroke.