ATP powers motor proteins through a cycle of binding, hydrolysis, and release, converting chemical energy into mechanical work. The reference describes this process specifically for myosin, a motor protein that interacts with actin filaments.
Myosin and Actin Interaction Powered by ATP
Myosin, a crucial motor protein, exemplifies how ATP drives movement. Here's a breakdown of the mechanism:
- ATP Binding: Each myosin head binds to ATP.
- ATP Hydrolysis: The myosin head hydrolyzes ATP into ADP and inorganic phosphate (Pi). This hydrolysis step energizes the myosin head, causing it to cock into a "high-energy" conformation.
- Binding to Actin: The energized myosin head binds to an actin filament.
- Power Stroke: The release of Pi and then ADP causes the myosin head to undergo a conformational change, the "power stroke," which pulls the actin filament relative to the myosin. This is where the mechanical work is performed.
- Release: The cycle resets when a new ATP molecule binds to the myosin head, causing it to detach from the actin filament.
This cycle repeats continuously as long as ATP is available, resulting in the sliding of actin filaments.
Efficiency and Orientation
The reference highlights the importance of the opposing orientation of myosin heads in thick filaments. This arrangement ensures:
- Efficient Sliding: The opposing orientation allows the thick filament to efficiently slide pairs of oppositely oriented actin filaments past each other.
- Continuous Movement: As one myosin head detaches, another is already bound to the actin filament, ensuring continuous movement.
Summary Table
| Step | Description | Energy Source | Result |
|---|---|---|---|
| ATP Binding | Myosin head binds to ATP. | ATP | Detachment from actin. |
| ATP Hydrolysis | ATP is hydrolyzed to ADP and Pi. | ATP | Myosin head cocks into a high-energy conformation. |
| Binding to Actin | Energized myosin head binds to actin. | - | Attachment to actin filament. |
| Power Stroke | Release of Pi and ADP; myosin head returns to its original conformation. | ADP and Pi | Sliding of actin filament; force generation. |
| Release | New ATP binds, causing detachment from actin and restarting the cycle. | ATP | Cycle reset. |
