Initiation of ERAD by the Bifunctional Complex of Mnl1/Htm1 Mannosidase and Protein Disulfide Isomerase

Overview

Journal Nat Struct Mol Biol

Date 2025 Feb 10

PMID 39930008

Authors

Dan Zhao

Xudong Wu

Tom A Rapoport

Affiliations

Soon will be listed here.

Abstract

Misfolded glycoproteins in the endoplasmic reticulum (ER) lumen are translocated into the cytosol and degraded by the proteasome, a conserved process called ER-associated protein degradation (ERAD). In Saccharomyces cerevisiae, the glycan of these proteins is trimmed by the luminal mannosidase Mnl1 (Htm1) to generate a degradation signal. Interestingly, Mnl1 is associated with protein disulfide isomerase (Pdi1). Here we used cryo-electron microscopy, biochemical and in vivo experiments to elucidate how this complex initiates ERAD. The Mnl1-Pdi1 complex first demannosylates misfolded, globular proteins that are recognized through the C-terminal domain (CTD) of Mnl1; Pdi1 causes the CTD to ignore completely unfolded polypeptides. The disulfides of these globular proteins are then reduced by the Pdi1 component of the complex. Mnl1 blocks the canonical oxidative function of Pdi1, allowing it to function as a disulfide reductase in ERAD. The generated unfolded polypeptides can then be translocated across the membrane into the cytosol.

References

Ruggiano A, Foresti O, Carvalho P . Quality control: ER-associated degradation: protein quality control and beyond. J Cell Biol. 2014; 204(6):869-79. PMC: 3998802. DOI: 10.1083/jcb.201312042. View

Christianson J, Jarosch E, Sommer T . Mechanisms of substrate processing during ER-associated protein degradation. Nat Rev Mol Cell Biol. 2023; 24(11):777-796. DOI: 10.1038/s41580-023-00633-8. View

Wu X, Rapoport T . Mechanistic insights into ER-associated protein degradation. Curr Opin Cell Biol. 2018; 53:22-28. PMC: 6131047. DOI: 10.1016/j.ceb.2018.04.004. View

Kumari D, Brodsky J . The Targeting of Native Proteins to the Endoplasmic Reticulum-Associated Degradation (ERAD) Pathway: An Expanding Repertoire of Regulated Substrates. Biomolecules. 2021; 11(8). PMC: 8393694. DOI: 10.3390/biom11081185. View

Bodnar N, Rapoport T . Toward an understanding of the Cdc48/p97 ATPase. F1000Res. 2017; 6:1318. PMC: 5543420. DOI: 10.12688/f1000research.11683.1. View

Nakatsukasa K, Nishikawa S, Hosokawa N, Nagata K, Endo T . Mnl1p, an alpha -mannosidase-like protein in yeast Saccharomyces cerevisiae, is required for endoplasmic reticulum-associated degradation of glycoproteins. J Biol Chem. 2001; 276(12):8635-8. DOI: 10.1074/jbc.C100023200. View

Quan E, Kamiya Y, Kamiya D, Denic V, Weibezahn J, Kato K . Defining the glycan destruction signal for endoplasmic reticulum-associated degradation. Mol Cell. 2008; 32(6):870-7. PMC: 2873636. DOI: 10.1016/j.molcel.2008.11.017. View

Clerc S, Hirsch C, Oggier D, Deprez P, Jakob C, Sommer T . Htm1 protein generates the N-glycan signal for glycoprotein degradation in the endoplasmic reticulum. J Cell Biol. 2009; 184(1):159-72. PMC: 2615083. DOI: 10.1083/jcb.200809198. View

Xie W, Ng D . ERAD substrate recognition in budding yeast. Semin Cell Dev Biol. 2010; 21(5):533-9. DOI: 10.1016/j.semcdb.2010.02.007. View

10.

JAKOB C, Bodmer D, Spirig U, Battig P, Marcil A, Dignard D . Htm1p, a mannosidase-like protein, is involved in glycoprotein degradation in yeast. EMBO Rep. 2001; 2(5):423-30. PMC: 1083883. DOI: 10.1093/embo-reports/kve089. View

11.

Kim W, Spear E, Ng D . Yos9p detects and targets misfolded glycoproteins for ER-associated degradation. Mol Cell. 2005; 19(6):753-64. DOI: 10.1016/j.molcel.2005.08.010. View

12.

Bhamidipati A, Denic V, Quan E, Weissman J . Exploration of the topological requirements of ERAD identifies Yos9p as a lectin sensor of misfolded glycoproteins in the ER lumen. Mol Cell. 2005; 19(6):741-51. DOI: 10.1016/j.molcel.2005.07.027. View

13.

Szathmary R, Bielmann R, Nita-Lazar M, Burda P, Jakob C . Yos9 protein is essential for degradation of misfolded glycoproteins and may function as lectin in ERAD. Mol Cell. 2005; 19(6):765-75. DOI: 10.1016/j.molcel.2005.08.015. View

14.

Gauss R, Jarosch E, Sommer T, Hirsch C . A complex of Yos9p and the HRD ligase integrates endoplasmic reticulum quality control into the degradation machinery. Nat Cell Biol. 2006; 8(8):849-54. DOI: 10.1038/ncb1445. View

15.

Wu X, Siggel M, Ovchinnikov S, Mi W, Svetlov V, Nudler E . Structural basis of ER-associated protein degradation mediated by the Hrd1 ubiquitin ligase complex. Science. 2020; 368(6489). PMC: 7380553. DOI: 10.1126/science.aaz2449. View

16.

Pisa R, Rapoport T . Disulfide-crosslink analysis of the ubiquitin ligase Hrd1 complex during endoplasmic reticulum-associated protein degradation. J Biol Chem. 2022; 298(9):102373. PMC: 9478403. DOI: 10.1016/j.jbc.2022.102373. View

17.

Pfeiffer A, Stephanowitz H, Krause E, Volkwein C, Hirsch C, Jarosch E . A Complex of Htm1 and the Oxidoreductase Pdi1 Accelerates Degradation of Misfolded Glycoproteins. J Biol Chem. 2016; 291(23):12195-207. PMC: 4933269. DOI: 10.1074/jbc.M115.703256. View

18.

Liu Y, Fujimori D, Weissman J . Htm1p-Pdi1p is a folding-sensitive mannosidase that marks N-glycoproteins for ER-associated protein degradation. Proc Natl Acad Sci U S A. 2016; 113(28):E4015-24. PMC: 4948361. DOI: 10.1073/pnas.1608795113. View

19.

Sakoh-Nakatogawa M, Nishikawa S, Endo T . Roles of protein-disulfide isomerase-mediated disulfide bond formation of yeast Mnl1p in endoplasmic reticulum-associated degradation. J Biol Chem. 2009; 284(18):11815-25. PMC: 2673250. DOI: 10.1074/jbc.M900813200. View

20.

Gauss R, Kanehara K, Carvalho P, Ng D, Aebi M . A complex of Pdi1p and the mannosidase Htm1p initiates clearance of unfolded glycoproteins from the endoplasmic reticulum. Mol Cell. 2011; 42(6):782-93. DOI: 10.1016/j.molcel.2011.04.027. View