Substrate-specific requirements for UGT1-dependent release from calnexin.
Newly synthesized glycoproteins displaying monoglucosylated N-glycans bind to the endoplasmic reticulum (ER) chaperone calnexin, and their maturation is catalyzed by the calnexin-associated oxidoreductase ERp57. Folding substrates are eventually released from calnexin, and terminal glucoses are removed from N-glycans. The UDP-glucose:glycoprotein glucosyltransferase (UGT1, UGGT, GT) monitors the folding state of polypeptides released from calnexin and adds back a glucose residue on N-glycans of nonnative polypeptides, thereby prolonging retention in the calnexin chaperone system for additional folding attempts. Here we show that for certain newly synthesized glycoproteins UGT1 deletion has no effect on binding to calnexin. These proteins must normally complete their folding program in one binding event. Other proteins normally undergo multiple binding events, and UGT1 deletion results in their premature release from calnexin. For other proteins, UGT1 deletion substantially delays release from calnexin, unexpectedly showing that UGT1 activity might be required for a structural maturation needed for substrate dissociation from calnexin and export from the ER.
Soldà
Tatiana
T
Institute for Research in Biomedicine, CH-6500 Bellinzona, Switzerland.
Galli
Carmela
C
Institute for Research in Biomedicine, CH-6500 Bellinzona, Switzerland.
Kaufman
Randal J
RJ
Howard Hughes Medical Institute, University of Michigan Medical Center, Ann Arbor, MI 48109, USA; Department of Biological Chemistry, University of Michigan Medical Center, Ann Arbor, MI 48109, USA.
Molinari
Maurizio
M
Institute for Research in Biomedicine, CH-6500 Bellinzona, Switzerland. Electronic address: maurizio.molinari@irb.unisi.ch.
D000818:Animals; D001483:Base Sequence; D001693:Biological Transport, Active; D037281:Calnexin / Q000378:metabolism*; D002478:Cells, Cultured; D017931:DNA Primers / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism; D006031:Glycosylation; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry / Q000378:metabolism; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D011485:Protein Binding; D017510:Protein Folding; D013379:Substrate Specificity; D014759:Viral Envelope Proteins / Q000737:chemistry / Q000378:metabolism
D017931:DNA Primers; C028391:G protein, vesicular stomatitis virus; D006023:Glycoproteins; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D008562:Membrane Glycoproteins; D014759:Viral Envelope Proteins; D037281:Calnexin; D014453:Glucuronosyltransferase