Molecular mechanism of the ATP synthase proton channel

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ATP synthase is a key enzyme of the energy metabolism in the vast majority of living organisms. It converts electrochemical energy stored in the form of transmembrane ion gradients into a pure chemical form of a high-energy bond in the adenosine triphosphate (ATP) molecule, which serves as a universal energy currency unit of the cell. ATP synthase functions as a molecular turbine driven by the transmembrane flow of protons through the membrane domain of the protein. The molecular mechanism of transformation of the energy of proton gradient into the kinetic energy of rotor movement is not well understood. While the high resolution structure of the rotor has been solved, the structure of the stator remains largely unknown. The long-term goal of this work is to elucidate the mechanism of proton transfer through the membrane channel of ATP synthase. We plan to analyze the structure of the proton channel using a combination of high-resolution nuclear magnetic resonance spectroscopy (NMR), X-ray crystallography, biochemical methods, and molecular modeling. We will use engineered proteins designed to model the essential structural elements of the proton channel to solve the structure by X-ray crystallography. This approach may offer an alternative to the attempts to solve the structure of the complete membrane domain of the ATP synthase, which so far have been unsuccessful. In parallel, we will continue investigation of the global fold of subunit 'a' by multidimensional NMR. The incremental structural information provided by NMR studies taken together with the large body of already available biochemical data will guide molecular modeling of the proton channel by restrained molecular dynamics until the high-resolution X-ray structure becomes available. NMR is a uniquely powerful tool for investigation of molecular dynamics of membrane proteins, as well as transient protein-lipid and protein-protein interactions. It can also provide valuable structural information, where protein crystallography fails. Investigation of subunit 'a' will advance application of high-resolution NMR to membrane proteins.