title: TFG clusters COPII-coated transport carriers and promotes early secretory pathway organization.
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.
authors.affiliation: Department of Biomolecular Chemistry, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI, USA.
authors.forename: Adam
authors.initials: A
authors.lastname: Johnson
authors.affiliation: Institute of Molecular Biophysics, Florida State University, Tallahassee, FL, USA.
authors.forename: Nilakshee
authors.initials: N
authors.lastname: Bhattacharya
authors.affiliation: Department of Biomolecular Chemistry, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Hanna
authors.affiliation: Departments of Botany and Genetics, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Janice G
authors.initials: JG
authors.lastname: Pennington
authors.affiliation: Department of Biomolecular Chemistry, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI, USA.
authors.forename: Amber L
authors.initials: AL
authors.lastname: Schuh
authors.affiliation: Department of Biomolecular Chemistry, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: Departments of Botany and Genetics, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Marisa S
authors.initials: MS
authors.lastname: Otegui
authors.affiliation: Institute of Molecular Biophysics, Florida State University, Tallahassee, FL, USA Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, USA.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Stagg
authors.affiliation: Department of Biomolecular Chemistry, University of Wisconsin-Madison School of Medicine and Public Health, Madison, WI, USA audhya@wisc.edu.
authors.forename: Anjon
authors.initials: A
authors.lastname: Audhya
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D022181:COP-Coated Vesicles / Q000378:metabolism*; D002460:Cell Line; D002522:Chlorocebus aethiops; D002942:Circular Dichroism; D018274:Electroporation; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D036681:Fluorescence Recovery After Photobleaching; D005455:Fluorescent Antibody Technique; D006801:Humans; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D046912:Multiprotein Complexes / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D055571:Secretory Pathway / Q000502:physiology*; D021601:trans-Golgi Network / Q000378:metabolism*; D033921:Vesicular Transport Proteins
chemical_list: D046912:Multiprotein Complexes; D011506:Proteins; D034741:RNA, Small Interfering; C096163:TFG protein, human; D033921:Vesicular Transport Proteins
keywords: COPII vesicle transport; intrinsic disorder; secretion; single particle electron microscopy