Browsing by Author "Desai, Tanvi"

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    Characterization of Structure and Function Relationship between Domains of the ER Membrane Protein Atlastin
    (2014-02-06) Desai, Tanvi; McNew, James A.; Huang, Huey W.; Braam, Janet; Stern, Michael; Lwigale, Peter Yunju
    The endoplasmic Reticulum (ER) is an important site for lipid synthesis, protein synthesis and transport. ER fusion is an essential process for its maintenance and biogenesis. Mutations in genes involved in this process cause Hereditary Spastic Paraplegia (HSP). These mutations are shown to affect intracellular trafficking and localization of membrane compartment. One of the important proteins causing early onset of HSP is Atlastin. Previous work in McNew lab at Rice University (Moss et al., 2011b) has shown that atlastin is involved in the homotypic fusion of the ER and the C-terminal cytoplasmic region of atlastin is essential for atlastin mediated fusion. During my studies presented in this thesis, I was able to demonstrate that the C-terminal cytoplasmic region of atlastin destabilizes lipid bilayers to facilitate fusion. The requirement of C-terminal cytoplasmic region is minimal when fusing two fluid (or unstable) lipid bilayers. The C-terminal cytoplasmic region of atlastin forms an amphipathic helix and mutations on the hydrophobic phase of the helix reduce fusion. These mutations are not dominant, as presence of full length atlastin on even one of the fusing lipid bilayers can significantly improve fusion during a heterotypic fusion reaction. Additionally, domain swaps between human atlastin-1 and drosophila atlastin show that the role of C-terminal cytoplasmic region is highly conserved. Also, during my research presented here in, I found that when the transmembrane region and C-terminal cytoplasmic region of human atlastin-1 were swapped with drosophila atlastin, it showed functional similarity. These results show that although atlastins in organisms play an important role in the ER fusion, there are likely species specific differences in how this is achieved. An understanding of atlastin mediated fusion should help in unraveling mechanisms of HSP pathogenesis and other disorders arising from dysfunctional ER.
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    The Atlastin C-terminal Tail is an Amphipathic Helix that Perturbs Bilayer Structure during Endoplasmic Reticulum Homotypic Fusion
    (American Society for Biochemistry and Molecular Biology, 2015) Faust, Joseph E.; Desai, Tanvi; Verma, Avani; Ulengin, Idil; Sun, Tzu-Lin; Moss, Tyler J.; Betancourt, Miguel A.; Huang, Huey W.; Lee, Tina; McNew, James A.
    Fusion of tubular membranes is required to form three-way junctions found in reticular subdomains of the endoplasmic reticulum (ER). The large GTPase Atlastin has recently been shown to drive ER membrane fusion and three-way junction formation. The mechanism of Atlastin-mediated membrane fusion is distinct from SNARE-mediated and many details remain unclear. In particular, the role of the amphipathic C-terminal tail of Atlastin is still unknown. We have found that a peptide corresponding to the Atlastin C-terminal tail binds to membranes as a parallel alpha helix, induces bilayer thinning, and increases acyl chain disorder. The function of the C-terminal tail is conserved in human Atlastin. Mutations in the C-terminal tail decrease fusion activity in vitro, but not GTPase activity, and impair Atlastin function in vivo. In the context of unstable lipid bilayers, the requirement for the C-terminal tail is abrogated. These data suggest that the C-terminal tail of Atlastin locally destabilizes bilayers to facilitate membrane fusion.