V-ATPase Structure, Function and Regulation
The focus of our laboratory is on understanding the structure, function and regulation of a novel family of ATP-dependent proton pumps known as the vacuolar ATPases (or V-ATPases). Acidification of intracellular compartments by the V-ATPases is important for such processes as receptor-mediated endocytosis, intracellular membrane traffic, protein processing and degradation and the coupled transport of small molecules, such as neurotransmitters. Acidic compartments also provide the entry point for disease causing agents such as influenza virus and anthrax toxin.
Figure 1. Shown are the main functions of intracellular V-ATPases. Taken from Nishi & Forgac, 2002.
V-ATPases in the plasma membrane of certain cells function in such processes as bone resorption, renal acidification and tumor metastasis. Our laboratory is interested in both the basic biochemistry and cell physiology of the V-ATPases as well as their role as potential targets in treating human diseases such as osteoporosis and cancer.
Figure 2. Shown are two of the functions of plasma membrane V-ATPases. Taken from Forgac, 2007.
The V-ATPases are large, multi-subunit complexes composed of a peripheral V1 domain that hydrolyzes ATP and an integral V0 domain that transports protons. These two activities are coupled via a rotary mechanism. We have employed a variety of biochemical and molecular biological approaches in both yeast and mammalian systems to probe the structure and mechanism of the V-ATPases. Among the questions that we are currently addressing is the mechanism by which protons are translocated through the V0 domain.
Figure 3. The structure of the V-ATPase complex is shown. Taken from Forgac, 2007.
We are also investigating how V-ATPase activity is controlled in vivo. An important mechanism of regulating V-ATPase activity in both yeast and mammalian systems is through reversible dissociation of the V1 and V0 domains. We have recently demonstrated that the Ras/cAMP/PKA pathway plays a crucial role in regulating in vivo assembly of the V-ATPase in yeast. We are currently exploring how PKA regulates V-ATPase assembly and whether PKA also regulates V-ATPase assembly in mammalian cells. Finally, we are exploring the role of V-ATPases in tumor cell metastasis and developing a high through-put screen to identify isoform-specific inhibitors of the V-ATPase that can serve as therapeutic drugs for the prevention of osteoporosis and cancer metastasis.
Figure 4. In vivo dissociation of the V-ATPase complex is shown. Taken from Forgac, 2007.