In addition to studies focused on elucidating the structure, mechanism, and regulation of the mammalian mitochondrial ATP synthase, a major disease focus for many years has been cancer because of its well known alterations in energy metabolism. More recently, we have entered also into a study of heart dysfunction as the heart with every beat is totally dependent on energy metabolism, with the mitochondrial ATP synthase being intimately involved.

The laboratory uses chemistry, molecular biology, biophysics, immunology, tissue culture and animal models to better understand the energetics/energy metabolism of normal and pathological cells/tissues. A major focus is on the two “power plants”, the mitochondria and the glucose catabolic system, as well as on the interaction between these two systems. The following problems are being studied:

1) The mechanism and regulation of ATP synthesis in mammalian mitochondria.
This involves the study of the molecular properties of the ATP synthase complex that consists of two nano-motors both of which are necessary to make ATP. In a collaborative study we have obtained the 3-D structure of one of the motors and are now working on the structure of the whole complex that consists of 17 subunit types and over 30 total subunits.

Recently we discovered that the ATP synthase is in complex formation with the transport system (carrier) for phosphate and the transport system for adenine nucleotides (ADP and ATP). We have named this complex the “ATP Synthasome” and are now carrying out studies to obtain a 3-D structure of the whole complex. It is important to note that the ATP synthasome represents the terminal complex of oxidative phosphorylation in mitochondria and makes most of the ATP needed/day to supply our energy needs.

In addition to these structural studies we are developing a yeast system to study the rotary parts of the two motors contained within the ATP synthasome. Significantly, it is these two nano-motors that when coupled drive ATP formation from ADP and Pi. This work has implications for nano-technology of the future as one of the two motors is driven by an electrochemical gradient, while the other is driven by ATP hydrolysis.

2) Cancer: Regulation and targeting genes and proteins responsible for the most common phenotype.
The most common phenotype of malignant cells including those derived from liver, breast, lung, brain, etc. is their capacity to utilize glucose at high rates. A key enzyme involved is hexokinase II that is markedly elevated and bound to the mitochondria. Not only does hexokinase II help couple ATP formation in mitochondria to the phosphorylation of glucose to “kick off” cancer cell glucose catabolism, its location on the mitochondria represses this organelle’s contribution to cell death. Therefore, hexokinase II in addition to its metabolic role also promotes cancer by helping immortalize cancer cells. We are studying the hexokinase II gene and developing novel strategies to target both the gene and the protein. We use both tissue culture and animal models. Recently we have identified a small molecule anticancer agent that has the capacity to eradicate advanced cancers in animal models without apparent toxic effects on the animals. We are now involved in the further development of this agent while searching for other effective anticancer agents.

3) Heart Dysfunction: Regulation of the mitochondrial ATP synthase in the normal and ischemic heart.
The heart can survive only short periods without oxygen. Conditions where oxygen is limiting can have grave consequences as the mitochondrial membrane potential will collapse and the mitochondrial ATP synthase will switch from synthesizing ATP to hydrolyzing ATP, thus depleting heart cells (cardiomyocytes) of the energy reserve they require for survival. Fortunately, the ATP synthase is well regulated in the heart so that the ATP hydrolytic event is minimized during short periods of ischemia (reduced oxygen). In fact, there are 3 known small peptide regulators of the ATP synthase, one which optimizes ATP synthesis and the other two that suppress ATP hydrolysis. In addition, the ATP synthase is subjected to signal transduction events that result either in its phosphorylation or dephosphorylation. We are currently initiating a project designed to understand the relative importance of these various regulatory events in protecting the heart during sudden ischemic insults.

[The laboratory has published over 200 papers of which >150 describe original research]

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