Sequential assistance of molecular chaperones and transient formation of covalent complexes during protein degradation from the ER.
BACE457 is a recently identified pancreatic isoform of human beta-secretase. We report that this membrane glycoprotein and its soluble variant are characterized by inefficient folding in the ER, leading to proteasome-mediated ER-associated degradation (ERAD). Dissection of the degradation process revealed that upon release from calnexin, extensively oxidized BACE457 transiently entered in disulfide-bonded complexes associated with the lumenal chaperones BiP and protein disulfide isomerase (PDI) before unfolding and dislocation into the cytosol for degradation. BACE457 and its lumenal variant accumulated in disulfide-bonded complexes, in the ER lumen, also when protein degradation was inhibited. The complexes were disassembled and the misfolded polypeptides were cleared from the ER upon reactivation of the degradation machinery. Our data offer new insights into the mechanism of ERAD by showing a sequential involvement of the calnexin and BiP/PDI chaperone systems. We report the unexpected transient formation of covalent complexes in the ER lumen during the ERAD process, and we show that PDI participates as an oxidoreductase and a redox-driven chaperone in the preparation of proteins for degradation from the mammalian ER.
Molinari
Maurizio
M
Institute for Research in Biomedicine, Via Vela 6, CH-6500 Bellinzona, Switzerland. maurizio.molinari@irb.unisi.ch
Galli
Carmela
C
Piccaluga
Verena
V
Pieren
Michel
M
Paganetti
Paolo
P
D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism; D010084:Oxidation-Reduction; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D021381:Protein Transport
D008562:Membrane Glycoproteins; D018832:Molecular Chaperones; D009097:Multienzyme Complexes; D053829:Amyloid Precursor Protein Secretases; D003546:Cysteine Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; D046988:Proteasome Endopeptidase Complex