title: Progressive quality control of secretory proteins in the early secretory compartment by ERp44.
abstract: ERp44 is a pH-regulated chaperone of the secretory pathway. In the acidic milieu of the Golgi, its C-terminal tail changes conformation, simultaneously exposing the substrate-binding site for cargo capture and the RDEL motif for ER retrieval through interactions with cognate receptors. Protonation of cysteine 29 in the active site allows tail movements in vitro and in vivo. Here, we show that conserved histidine residues in the C-terminal tail also regulate ERp44 in vivo. Mutants lacking these histidine residues retain substrates more efficiently. Surprisingly, they are also O-glycosylated and partially secreted. Co-expression of client proteins prevents secretion of the histidine mutants, forcing tail opening and RDEL accessibility. Client-induced RDEL exposure allows retrieval of proteins from distinct stations along the secretory pathway, as indicated by the changes in O-glycosylation patterns upon overexpression of different partners. The ensuing gradients might help to optimize folding and assembly of different cargoes. Endogenous ERp44 is O-glycosylated and secreted by human primary endometrial cells, suggesting possible pathophysiological roles of these processes.
authors.affiliation: Divisions of Genetics and Cell Biology and Immunology, Transplantation and Infectious Diseases, IRCCS Ospedale San Raffaele, 20132 Milan, Italy Department of Bioscience, Università degli Studi di Milano, Via Celoria 26, 20133 Milan, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Sannino
authors.affiliation: Divisions of Genetics and Cell Biology and Immunology, Transplantation and Infectious Diseases, IRCCS Ospedale San Raffaele, 20132 Milan, Italy Università Vita-Salute San Raffaele, 20132 Milan, Italy.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Anelli
authors.affiliation: Divisions of Genetics and Cell Biology and Immunology, Transplantation and Infectious Diseases, IRCCS Ospedale San Raffaele, 20132 Milan, Italy.
authors.forename: Margherita
authors.initials: M
authors.lastname: Cortini
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Shoji
authors.initials: S
authors.lastname: Masui
authors.affiliation: Divisions of Genetics and Cell Biology and Immunology, Transplantation and Infectious Diseases, IRCCS Ospedale San Raffaele, 20132 Milan, Italy Università Vita-Salute San Raffaele, 20132 Milan, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Degano
authors.affiliation: Divisions of Genetics and Cell Biology and Immunology, Transplantation and Infectious Diseases, IRCCS Ospedale San Raffaele, 20132 Milan, Italy Università Vita-Salute San Raffaele, 20132 Milan, Italy.
authors.forename: Claudio
authors.initials: C
authors.lastname: Fagioli
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Inaba
authors.affiliation: Divisions of Genetics and Cell Biology and Immunology, Transplantation and Infectious Diseases, IRCCS Ospedale San Raffaele, 20132 Milan, Italy Università Vita-Salute San Raffaele, 20132 Milan, Italy r.sitia@hsr.it.
authors.forename: Roberto
authors.initials: R
authors.lastname: Sitia
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D011786:Quality Control; D055571:Secretory Pathway
chemical_list: D002352:Carrier Proteins; C451899:ERP44 protein, human; D008565:Membrane Proteins; D018832:Molecular Chaperones
keywords: ERp44; Endoplasmic reticulum; Golgi; O-glycosylation; Protein quality control; Protein secretion
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