EDEM1 regulates ER-associated degradation by accelerating de-mannosylation of folding-defective polypeptides and by inhibiting their covalent aggregation.
Proteins expressed in the endoplasmic reticulum (ER) are covalently modified by co-translational addition of pre-assembled core glycans (glucose(3)-mannose(9)-N-acetylglucosamine(2)) to asparagines in Asn-X-Ser/Thr motifs. N-Glycan processing is essential for protein quality control in the ER. Cleavages and re-additions of the innermost glucose residue prolong folding attempts in the calnexin cycle. Progressive loss of mannoses is a symptom of long retention in the ER and elicits preparation of terminally misfolded polypeptides for dislocation into the cytosol and proteasome-mediated degradation. The ER stress-induced protein EDEM1 regulates disposal of folding-defective glycoproteins and has been described as a mannose-binding lectin. Here we show that elevation of the intralumenal concentration of EDEM1 accelerates ER-associated degradation (ERAD) by accelerating de-mannosylation of terminally misfolded glycoproteins and by inhibiting formation of covalent aggregates upon release of terminally misfolded ERAD candidates from calnexin. Acceleration of Man(9) or Man(5)N-glycans dismantling upon overexpression was fully blocked by substitution in EDEM1 of one catalytic residue conserved amongst alpha1,2-mannosidases, thus suggesting that EDEM1 is an active mannosidase. This mutation did not affect the chaperone function of EDEM1.
Olivari
Silvia
S
Institute for Research in Biomedicine, CH-6500 Bellinzona, Switzerland.
Cali
Tito
T
Salo
Kirsi E H
KE
Paganetti
Paolo
P
Ruddock
Lloyd W
LW
Molinari
Maurizio
M
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008358:Mannose / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D010455:Peptides / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding
C486654:EDEM1 protein, human; D008565:Membrane Proteins; D010455:Peptides; D008358:Mannose