TFG clusters COPII‐coated transport carriers and promotes early secretory pathway organization |
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Authors: | Adam Johnson Nilakshee Bhattacharya Michael Hanna Janice G Pennington Amber L Schuh Lei Wang Marisa S Otegui Scott M Stagg Anjon Audhya |
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Affiliation: | 1. Department of Biomolecular Chemistry, University of Wisconsin‐Madison School of Medicine and Public Health, Madison, WI, USA;2. Institute of Molecular Biophysics, Florida State University, Tallahassee, FL, USA;3. Departments of Botany and Genetics, University of Wisconsin‐Madison, Madison, WI, USA;4. Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, USA |
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Abstract: | In mammalian cells, cargo‐laden secretory vesicles leave the endoplasmic reticulum (ER) en route to ER‐Golgi intermediate compartments (ERGIC) in a manner dependent on the COPII coat complex. We report here that COPII‐coated transport carriers traverse a submicron, TFG (Trk‐fused gene)‐enriched zone at the ER/ERGIC interface. The architecture of TFG complexes as determined by three‐dimensional electron microscopy reveals the formation of flexible, octameric cup‐like structures, which are able to self‐associate to generate larger polymers in vitro. In cells, loss of TFG function dramatically slows protein export from the ER and results in the accumulation of COPII‐coated carriers throughout the cytoplasm. Additionally, the tight association between ER and ERGIC membranes is lost in the absence of TFG. We propose that TFG functions at the ER/ERGIC interface to locally concentrate COPII‐coated transport carriers and link exit sites on the ER to ERGIC membranes. Our findings provide a new mechanism by which COPII‐coated carriers are retained near their site of formation to facilitate rapid fusion with neighboring ERGIC membranes upon uncoating, thereby promoting interorganellar cargo transport. |
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Keywords: | COPII vesicle transport intrinsic disorder secretion single particle electron microscopy |
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