Energy from the sun is entrapped by photosynthesis and stored in high energy compounds that we consume in food. The energy is released by controlled burning in the mitochondria in the cells of our bodies, and stored in the high energy compound adenosine triphosphate, ATP, the fuel of biology. ATP is made in the mitochondria inside our cells. They are “power stations” full of millions of molecular turbines, the ATP synthases that rotate like man-made turbines and churn out ATP in massive quantities. We understand most of how these molecular turbines work, but not how rotation is generated. This project will provide the missing information. Bacteria have turbines that differ significantly from the human ones, and they are controlled by different mechanisms. We want to understand these differences in structure, function and regulation so as to devise drugs to kill pathogenic bacteria by stopping their turbines without influencing the human ones.

Technical Abstract:
The F-ATP synthases in eubacteria and mitochondria are rotary machines with many common features. We will build on past achievements to extend fundamental knowledge about them and provide a basis for putting that knowledge to practical use. The mechanism of their catalytic domains is well understood, but how rotation is generated from the transmembrane proton-motive force is less clear. We will provide a molecular explanation of the generation of rotation. We intend to exploit mechanistic differences between human and bacterial enzymes to develop new drugs. One difference concerns their mechanisms of regulation. The mitochondrial enzyme is regulated by the inhibitor protein, IF1; in vitro, it inhibits ATP hydrolysis and not ATP synthesis, but its in vivo role is unclear, except that it inhibits the hydrolase activity of assembly intermediates. It may also inhibit in vivo ATP synthesis by a mechanism that we will investigate possible involving other unidentified proteins. Different regulatory mechanisms operate in eubacteria; for example in Mycobacteria, the enzyme can only make ATP and not hydrolyze it, but we do not yet know how hydrolysis is prevented. Eubacterial and mitochondrial enzymes differ also in their subunit compositions. They have a common core set to allow them to make ATP, but the mammalian mitochondrial enzymes have a "supernumerary" set of seven membrane proteins, each with a single predicted transmembrane a-helix. In mitochondria, these supernumerary subunits form an interface between monomeric complexes in the dimeric arrangements found in the inner membranes of the organelle. We are determining the structure of the dimeric complex to gain detailed information about how the membrane domain of the enzyme functions. As part of a wider collaboration we will study how the human ATP synthase is assembled.