Abstract
Sec61β, a subunit of the Sec61 translocon complex, is not essential in yeast and commonly used as a marker of endoplasmic reticulum (ER). In higher eukaryotes, such as Drosophila, deletion of Sec61β causes lethality, but its physiological role is unclear. Here, we show that Sec61β interacts directly with microtubules. Overexpression of Sec61β containing small epitope tags, but not a RFP tag, induces dramatic bundling of the ER and microtubule. A basic region in the cytosolic domain of Sec61β is critical for microtubule association. Depletion of Sec61β induces ER stress in both mammalian cells and Caenorhabditis elegans, and subsequent restoration of ER homeostasis correlates with the microtubule binding ability of Sec61β. Loss of Sec61β causes increased mobility of translocon complexes and reduced level of membrane-bound ribosomes. These results suggest that Sec61β may stabilize protein translocation by linking translocon complex to microtubule and provide insight into the physiological function of ER-microtubule interaction.
Highlights
In eukaryotic cells, the endoplasmic reticulum (ER) is composed of membrane tubules and sheets (Shibata et al, 2006)
These results suggest that Sec61β may interact with microtubules and the binding can be prevented with a large tag at the N-terminus
We show that Sec61β interacts directly with microtubules, and is involved in the maintenance of ER homeostasis
Summary
The endoplasmic reticulum (ER) is composed of membrane tubules and sheets (Shibata et al, 2006). The cisternal spacing is regulated by Climp (Shibata et al, 2010), which is proposed to be a luminal bridge, and the surface of the sheets are kept flat, likely by kinectin and p180, which scaffold the membrane as a rod-like structure (Shibata et al, 2010; Zhang and Hu, 2016). Tubules are likely involved in membrane trafficking, lipid metabolism, organelle contact, and stress sensing (Wang et al, 2017), whereas sheets are mostly locations for protein synthesis (Shibata et al, 2006; Voeltz et al, 2002). Sec and its associating proteins are enriched in ER sheets (Shibata et al, 2010)
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