Snapshots of a cellular motor
The enzyme ATP synthase spins like a wheel to convert energy into ATP for storage. High-speed imaging reveals the details of the rotation.
ATP synthase produces ATP using energy derived from proton gradients created during respiration or photosynthesis. The enzyme consists of two rotary motors, called F0 and F1. F0 is embedded in the membranes of energy-generating cellular structures, such as mitochondria, and is coupled through a common central shaft to F1, which protrudes from the membrane. Protons pumped through the F0 rotor are used to drive the rotation of F1 catalysing the production of ATP from ADP and inorganic phosphate. In 19 April Nature Ryohei Yasuda and colleagues of the Teikyo University Biotechnology Center in Kawasaki, Japan explain the details of the rotation of the F1 motor (Nature 2001, 410:898-904).
Yasuda et al attached a string of 40nm gold beads to the rotating shaft of F1 molecules that had been detached from the mitochondrial membrane. High-speed imaging was used to photograph the movement of the beads during the rotation of F1. Under these conditions F1 is capable only of hydrolysing ATP (hence, the name F1-ATPase). In the presence of ATP, F1 rotated in discrete 120° steps, composed of two smaller 90° and 30° substeps, each taking only a fraction of a millisecond. ATP binding drives the 90° substep. The 30° substep is thought to be driven by the release of a hydrolysis product.
"It's a remarkable accomplishment that we can now look at this internal mechanism," says Mark Schnitzer in an accompanying News and Views article.