ATP Synthase

The world's smallest biological electric motor

John Miller, Sladjana Maric, M. Scoppa, and M. Cheung,
Department of Physics,
University of Houston
Houston, Texas

Positive (blue) & negative (red) potential regions of ATP synthase. 1st image: deprotonated rotor (lacking extra protons) and part of the stator (left). 2nd & 3rd images: c-ring monomer, in which extra proton is either missing (deprotonated, 2nd image) or attached (protonated, 3rd image).

Every cell in our body contains millions of tiny electric motors, known as ATP synthase. These rotary motors are located in the inner membranes of mitochondria, our cellular powerhouses, and produce molecules of ATP (adenosine triphosphate) – the chemical packets of energy used by the muscles and other organs.  

A rotating part, known as the rotor or c-ring, drives a camshaft-like stalk to pry loose three ATP molecules per cycle from another part of the enzyme known as F1. Physicists at the University of Houston are studying how an electric field drives the c-ring to rotate. Positively charged protons pass through a channel in the a-subunit, which acts as the motor's stator, and attach to the c-ring.  

After completing nearly a full revolution, each proton exits to the other side of the membrane through another channel in the a-subunit. The images show regions of positive (blue) and negative (red) electrostatic potential created by positive and negative charges.  

The first image shows a deprotonated c-ring (lacking extra protons) and part of the a-subunit (left side). The second and third images show a small piece (monomer) of the c-ring, in which the extra proton is either missing (deprotonated, 2nd image), resulting in negative (red) potential, or attached (protonated, 3rd image), creating the positive (blue) region. The electric field lines emanating from the stator channels, similar to the magnetic field created by a bar magnet, act on protonated sites around the c-ring and a deprotonated site between the channels, and cause the ring to rotate like the rotor of an electric motor.

References

Humphrey, W., Dalke, A. and Schulten, K., "VMD - Visual Molecular Dynamics", J. Molec. Graphics, vol. 14, pp. 33-38 (1996).  

Baker NA, Sept D, Joseph S, Holst MJ, McCammon JA. “Electrostatics of nanosystems: application to microtubules and the ribosome.” Proc. Natl. Acad. Sci. USA 98, 10037-10041 (2001).  

Dolinsky TJ, Nielsen JE, McCammon JA, Baker. “NA. PDB2PQR: an automated pipeline for the setup, execution, and analysis of Poisson-Boltzmann electrostatics calculations.” Nucleic Acids Res, 32, W665-W667 (2004).  

Dolinsky TJ, Czodrowski P, Li H, Nielsen JE, Jensen JH, Klebe G, Baker NA. “PDB2PQR: Expanding and upgrading automated preparation of biomolecular structures for molecular simulations.” Nucleic Acids Res, 35, W522-5 (2007).

Usage Information

Reporters may freely use this image as long as they include the following credit: "Image courtesy of S. Maric and J. H. Miller/University of Houston".

For further information, contact:
Jason Bardi
(301) 209-3091