Reversible dissociation of the yeast V-ATPase and characterization of the N-terminal domain of subunit a. Jie Qi

ISBN: 9780549536628

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118 pages


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Reversible dissociation of the yeast V-ATPase and characterization of the N-terminal domain of subunit a.  by  Jie Qi

Reversible dissociation of the yeast V-ATPase and characterization of the N-terminal domain of subunit a. by Jie Qi
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The vacuolar (H+)-ATPases (V-ATPases) are a family of proton pumps that transport protons out of the cytoplasm into the lumen of intracellular compartments or the extracellular environment driven by ATP hydrolysis. V-ATPases function in many cellularMoreThe vacuolar (H+)-ATPases (V-ATPases) are a family of proton pumps that transport protons out of the cytoplasm into the lumen of intracellular compartments or the extracellular environment driven by ATP hydrolysis.

V-ATPases function in many cellular compartments such as endosomes, lysosomes and secretory vesicles, as well as the plasma membrane of specialized cells, such as renal intercalated cells and osteoclasts. Acidification of intracellular compartments is important for processes like membrane traffic, coupled transport of small molecules and viral infection while plasma membrane V-ATPases are important for renal acidification, bone resorption and tumor cell invasion. V-ATPases are composed of a peripheral domain (V1) that hydrolyzes ATP and an integral domain (V0) that transports protons and they operate by a rotary mechanism.

V-ATPase activity is regulated in vivo by a number of mechanisms, including reversible dissociation of V1 and V0 and selective targeting of V-ATPases. In yeast reversible dissociation happens when glucose is removed from the media. The first part of my thesis focused on understanding how in vivo dissociation depends on cellular environment and isoforms of subunit a, which target the V-ATPase to different cellular compartments. My results show that in vivo dissociation is very dependent on cellular environment but not so influenced by a subunit isoform.

After dissociation, the free V 0 is not permeable to protons, which is important in vivo. I next tested the hypothesis that the hydrophilic N-terminal domain of subunit a blocks passive proton flow by interacting with rotor subunits in free V 0. By preventing rotation of these subunits, passive proton transport would be blocked. My results show that the N-terminal domain of subunit a can be removed and the free V0 domain still does not leak protons. Cleavage between the N and C-terminal domains does cause partial uncoupling of proton transport and ATP hydrolysis.

These results suggest that the N-terminal domain of subunit a is not necessary to block passive proton transport through free V0 but that tight coupling of proton transport and ATP hydrolysis requires an intact subunit a.



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