Functional Characterization of Atlastins in Endoplasmic Reticulum Membrane Fusion

Abstract

The endoplasmic reticulum (ER), an essential organelle in eukaryotic cells, mediates various cellular processes, including cytoplasmic calcium level control, protein quality control, and lipid synthesis. These functions are thought to be closely related to the unique structure of the ER, which forms a network of sheets and tubules that are maintained by homotypic ER membrane fusion. Although the exact mechanism of homotypic ER fusion is yet to be clarified, the dynamin-like GTPase atlastin, an evolutionarily conserved protein family, is believed to mediate homotypic ER fusion at three-way junctions of the ER tubular network. In my dissertation, I focus on elucidating the mechanism of ER membrane fusion by atlastin of different species via various techniques. In the first part, I describe molecular mechanisms underlying membrane tethering and fusion by yeast atlastin Sey1p using a FRET-based single liposome fusion assay. This chapter dissects the molecular process of membrane fusion by Sey1p, examining the precise steps of Sey1p induced fusion. In the second part, the molecular mechanisms of membrane fusion by human atlastins (ATL1, ATL2 and ATL3) are investigated and verified via various fusion assays. This dissertation provides insight into the evolutionarily conserved mechanisms underlying formation and maintenance of the ER structure.