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How a Molecular Motor Minimizes Energy Waste
Turning a biologically important molecular motor at a constant rate saves energy, according to experiments.
APS/ Alan Stonebraker Energy factory. The enzyme ATP synthase consists of two motors, F o (orange) and F 1 (blue). The enzyme takes in molecular ingredients (shown in red on the left) and assembles them into the molecule ATP, which delivers energy to other parts of the cell (right). F o is embedded in a membrane (green) and is powered by a flow of protons (blue dots), which generates a torque on the shaft in the middle of F 1 . To explore this mechanism, researchers have replaced F o with an artificial motor.
APS/ Alan Stonebraker Energy factory. The enzyme ATP synthase consists of two motors, F o (orange) and F 1 (blue). The enzyme takes in molecular ingredients (shown in red on the left) and assembles them into the molecule ATP, which delivers energy to other parts of the cell (right). F o is embedded in a membrane (green) and is powered by a flow of protons (blue dots), which generates a torque on the shaft in the middle of F 1 . To explore this mechanism, researchers have replaced F o with an artificial motor. ×
Within every biological cell is an enzyme, called adenosine triphosphate (ATP) synthase, that churns out energy-rich molecules for fueling the cell’s activity. New experiments investigate the functioning of this “energy factory” by artificially cranking one of the enzyme’s molecular motors [1]. The results suggest that maintaining a fixed rotation rate minimizes energy waste caused by microscopic fluctuations. Future work could confirm the role of efficiency in the evolutionary design of biological motors.
ATP synthase consists of two rotating molecular motors, F o and F 1 , that are oriented along a common rotation axis and locked together so that the rotation of F o exerts a torque on the shaft in the middle of F 1 . The resulting motion within F 1 helps bring together the chemical ingredients of the molecule ATP, which stores energy that can later be used in cellular processes.
Researchers have determined the motors’ atomic structures, but the details of the coupling between F o and F 1 are unclear. F o is embedded in a membrane. Protons flow across this membrane and drive F o ’s rotation, but directly measuring F o ’s torque is challenging because it would require reproducing the membrane and its chemical environment in a controllable laboratory setting, says Shoichi Toyabe of Tohoku University in Japan.
Toyabe and his colleagues devised an approach for overcoming this challenge. They reasoned that F o could exert torque on F 1 in different ways, but evolution would favor a more energetically efficient driving mechanism. To explore the role of efficiency, the team replaced F o with an artificial motor and used it to drive F 1 ’s rotation in one of two ways: either by applying constant torque or by fixing the rotation rate with a variable torque. Artificially rotating the F 1 motor is not new, but no one has previously been able to drive the motor in two distinct modes and measure their efficiencies.
et al. [1] T. Mishima Bionic manipulator. This sketch of the experimental setup shows the F 1 motor fixed beneath a glass slide. Two plastic beads, attached to the motor’s shaft, rotate in response to the electric field generated by a set of four electrodes below.
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