Question

The movement of molecular motors depends on the conformational changes that the proteins undergo as they proceed through the cycle of nucleotide binding, hydrolysis, and release. If you were to add a nonhydrolyzable form of ATP to myosin, at what point would you block its movement? How is this similar to or different from adding a nonhydrolyzable form of ATP to kinesin?

Answer 1

Muscles contract in a repeated pattern of binding and releasing between the two thin and thick strands of the sarcomere. ATP is critical to prepare myosin for binding to the actin filament. Binding of ATP to myosin results in moving myosin at high-energy state. Later, ATP is hydrolyzed into ADP and inorganic phosphate (P_i) by the enzyme ATPase that results in changing the angle of the myosin head into a “cocked” position, ready to bind to actin if the sites are available. At this stage, ADP and Pi remain attached to myosin. The release of Pi after binding of myosin with actin (Regulated by Calcium) result in power stroke for the contraction of the muscle.

Use of nonhydrolyzable form of ATP will bring myosin at high energy state but will block the angling of the myosin head into a cocked position as it will require energy released by the action of ATPase on the bound ATP.

Though Kinesin and Myosin are motor proteins, there are certain structural and functional differences between them. Kinesin is the motor protein found in all vertebrates. It occurs in both neuronal and non-neuronal cells.The Kinesin motor molecule moves along microtubules by interacting with the tubular protein. Kinesin is responsible for fast axonal transport, formation of spindle apparatus and separation of chromosomes during mitosis and meiosis and transport of membrane bound organelles. These action is driven by ATP hydrolysis. ATP bind with the Kinesin and bring it into active state ATP hydrolysis results in bending of Kinesin head and attactment with microtubules . That means use of nonhydrolyzable form of ATP will activate the Kinesin head but will block the bending of Kinesin.