Biology and Biomedical Sciences: Biochemistry
Date of Award
Doctor of Philosophy (PhD)
Chair and Committee
AAA+ ATPase enzymes couple ATP hydrolysis to the exertion of conformational change on a substrate. TorsinA is one of the few AAA+ ATPases that resides within the lumen of the mammalian endoplasmic reticulum: ER). A glutamic acid deletion in the catalytic domain of torsinA causes DYT1 dystonia, but torsinA's function and the basis for disease remain unclear. I show that torsinA is dynamically targeted from the bulk ER to nuclear envelope: NE) upon coexpression with a cofactor protein, LULL1, and that torsinA's movement into the NE is concomitant with displacement of select linker of the nucleoskeleton and cytoskeleton: LINC) complex proteins. These effects suggest a role for torsinA in modulating nuclear positioning via the LINC proteins. The DYT1 mutant also responds to LULL1, but only weakly displaces LINC proteins. These findings identify a possible mechanism for regulating torsinA localization and activity via LULL1, and suggest that activity at the NE is perturbed by the disease-causative mutation. An N-terminal hydrophobic domain: NTD) in torsinA is required for NE targeting. Surprisingly, deletion of this domain also abolishes retention of torsinA within the ER. I demonstrate that the NTD mediates stable monotopic association with the lumenal leaflet of the ER, which in turn controls ER retention. Membrane domains from certain other ER resident proteins are thought to control targeting by selective partitioning within the membrane. I propose that this lipid-based sorting mechanism extends to monotopic membrane proteins, and identify a group of proteins that may share torsinA's topology and ER retention mechanism. Returning to the interaction between torsinA and LULL1, I identify distinct regions of LULL1 that are responsible for torsinA binding and re-targeting to the NE. A conserved helix at the extreme C terminus of LULL1 mediates its interaction with torsinA, while the extreme N terminus of LULL1 must be present in order for torsinA to be targeted to the NE. Importantly, the N terminus of LULL1 is cytosolic, while the C-terminal torsinA-binding domain is lumenal, raising the intriguing possibility that control of torsinA localization involves communication between the cytosol and the ER lumen. The work in this thesis provides new insight to torsinA's cellular function and dysfunction in disease and defines novel mechanisms of controlling localization of membrane proteins.
Vander Heyden, Abigail, "Targeting and activity of the AAA+ ATPase torsinA within the endoplasmic reticulum" (2011). All Theses and Dissertations (ETDs). 655.