Myosin type V is a two-headed myosin that operates as a transport motor to move
ID: 817765 • Letter: M
Question
Myosin type V is a two-headed myosin that operates as a transport motor to move its attached cargo along actin filaments. Its mechanism is similar to that of muscle myosin, but its acts positvely, like kinesin. The reactiion cycle diagrammed here (ABOVE PICTURE) begins with both myosin V heads bound to an actin filament. ADP is bound to the leading head, and the nucleotide-binding site in the trailing head is empty.
(a) Based on your knowledge of the muscle myosin reaction cycle, propose a reaction mechanism for myosin V, starting with the entry of ATP.
(b) How does each step of the ATP hydrolysis reaction correspond to a conformational change in myosin V?
Myosin type V is a two-headed myosin that operates as a transport that operates as a transport motor to move its attached cargo along actin filaments. Its mechanism is similar to that of muscle myosin, but it acts processively, like kinesin. The reaction cycle diagrammed here begins with both myosin V heads bound to an action filament. ADP is bound to the leading head, and the nucleotide-binding site in the trailing head is empty. Based on your knowledge of the muscle myosin reaction cycle (Fig. 5.35), propose a reaction mechanism for myosin V, starting with the entry of ATP. How does each step of the ATP hydrolysis reaction correspond to a conformational change in myosin V?Explanation / Answer
From the diagram we can conclude that when ATP binds to the mysoin V molecule, the head that is not leading (yellow) undergoes a conformational change that causes it to unbind from actin and swivel around to become the new leading head. As ATP is cleaved into ADP it causes the new leading molecule (yellow) to bind to the actin. The yellow head is now the new leading head and the process repeats once more; each time an ATP molecule binds and is cleaved the not leading head swivels around and attatches so it moves progressively in this fashion and shortens the muscle fiber.
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