title: Identification of ERGIC-53 as an intracellular transport receptor of alpha1-antitrypsin.
abstract: Secretory proteins are exported from the endoplasmic reticulum (ER) by bulk flow and/or receptor-mediated transport. Our understanding of this process is limited because of the low number of identified transport receptors and cognate cargo proteins. In mammalian cells, the lectin ER Golgi intermediate compartment 53-kD protein (ERGIC-53) represents the best characterized cargo receptor. It assists ER export of a subset of glycoproteins including coagulation factors V and VIII and cathepsin C and Z. Here, we report a novel screening strategy to identify protein interactions in the lumen of the secretory pathway using a yellow fluorescent protein-based protein fragment complementation assay. By screening a human liver complementary DNA library, we identify alpha1-antitrypsin (alpha1-AT) as previously unrecognized cargo of ERGIC-53 and show that cargo capture is carbohydrate- and conformation-dependent. ERGIC-53 knockdown and knockout cells display a specific secretion defect of alpha1-AT that is corrected by reintroducing ERGIC-53. The results reveal ERGIC-53 to be an intracellular transport receptor of alpha1-AT and provide direct evidence for active receptor-mediated ER export of a soluble secretory protein in higher eukaryotes.
authors.affiliation: Biozentrum, University of Basel, CH-4056 Basel, Switzerland.
authors.forename: Beat
authors.initials: B
authors.lastname: Nyfeler
authors.forename: Veronika
authors.initials: V
authors.lastname: Reiterer
authors.forename: Markus W
authors.initials: MW
authors.lastname: Wendeler
authors.forename: Eduard
authors.initials: E
authors.lastname: Stefan
authors.forename: Bin
authors.initials: B
authors.lastname: Zhang
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Michnick
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Hauri
mesh_terms: D000818:Animals; D001681:Biological Assay; D019556:COS Cells; D002241:Carbohydrates / Q000737:chemistry; D002522:Chlorocebus aethiops; D015536:Down-Regulation / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005347:Fibroblasts; D015723:Gene Library; D006367:HeLa Cells; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism*; D008164:Luminescent Proteins; D037241:Mannose-Binding Lectins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D040901:Proteomics / Q000379:methods; D000515:alpha 1-Antitrypsin / Q000378:metabolism*
chemical_list: D002241:Carbohydrates; C084004:LMAN1 protein, human; D008164:Luminescent Proteins; D037241:Mannose-Binding Lectins; D008565:Membrane Proteins; D000515:alpha 1-Antitrypsin