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Glycosylation-directed quality control of protein folding

Key Points

  • Protein glycosylation describes various conserved post-translational modifications. Although some proteins can be glycosylated in the cytosol, glycosylation is most prevalent in the secretory pathway, in which it is involved in many processes.

  • Proteins that are synthesized at the endoplasmic reticulum (ER) membranes can be glycosylated at Asn, Ser and Thr residues. These can be further modified in the Golgi apparatus.

  • The core N-linked glycan has a branched structure composed of Glc3Man9GlcNAc2, which is trimmed sequentially by ER glycosidases. The trimming events coordinate folding and quality control factors to ensure high-fidelity production of mature glycoproteins.

  • Trimming of an N-linked glycan to the Man7GlcNAc2 structure bearing a terminal α-1,6-linked mannose residue attached to an unfolded peptide allows peptide recognition by the yeast osteosarcoma 9 (Yos9) ER-associated degradation (ERAD) receptor. This initiates peptide retro-translocation and degradation by the ubiquitin–proteasome system.

  • In budding yeast, misfolded proteins are modified by O-mannosylation by the Pmt1–Pmt2 complex. This modification can facilitate ERAD or promote the transport of the substrate out of the ER to the vacuole or cell surface.

  • O-mannosylation is used in budding yeast to terminate futile cycles of protein folding to facilitate their entry into ERAD and relieve ER stress.


Membrane-bound and soluble proteins of the secretory pathway are commonly glycosylated in the endoplasmic reticulum. These adducts have many biological functions, including, notably, their contribution to the maturation of glycoproteins. N-linked glycans are of oligomeric structure, forming configurations that provide blueprints to precisely instruct the folding of protein substrates and the quality control systems that scrutinize it. O-linked mannoses are simpler in structure and were recently found to have distinct functions in protein quality control that do not require the complex structure of N-linked glycans. Together, recent studies reveal the breadth and sophistication of the roles of these glycan-directed modifications in protein biogenesis.

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Figure 1: Glycan precursors in the endoplasmic reticulum.
Figure 2: The Doa10 and HMG-CoA reductase degradation 1 (Hrd1) endoplasmic reticulum (ER)-associated degradation (ERAD) complexes and their downstream effectors.
Figure 3: N-linked glycan trimming in the endoplasmic reticulum (ER).
Figure 4: N-glycan directed protein folding and quality control.
Figure 5: The unfolded protein O-mannosylation pathway.


  1. 1

    Park, E. & Rapoport, T. A. Mechanisms of Sec61/SecY-mediated protein translocation across membranes. Annu. Rev. Biophys. 41, 21–40 (2012).

    CAS  Article  Google Scholar 

  2. 2

    Gidalevitz, T., Stevens, F. & Argon, Y. Orchestration of secretory protein folding by ER chaperones. Biochim. Biophys. Acta 1833, 2410–2424 (2013).

    CAS  PubMed  PubMed Central  Google Scholar 

  3. 3

    Braakman, I. & Hebert, D. N. Protein folding in the endoplasmic reticulum. Cold Spring Harb. Perspect. Biol. 5, a013201 (2013).

    PubMed  PubMed Central  Google Scholar 

  4. 4

    Araki, K. & Nagata, K. Protein folding and quality control in the ER. Cold Spring Harb. Perspect. Biol. 4, a015438 (2012).

    PubMed  PubMed Central  Google Scholar 

  5. 5

    Kelleher, D. J. & Gilmore, R. An evolving view of the eukaryotic oligosaccharyltransferase. Glycobiology 16, 47R–62R (2006).

    CAS  Google Scholar 

  6. 6

    Lizak, C., Gerber, S., Numao, S., Aebi, M. & Locher, K. P. X-ray structure of a bacterial oligosaccharyltransferase. Nature 474, 350–355 (2011).

    CAS  PubMed  Google Scholar 

  7. 7

    Ruiz-Canada, C., Kelleher, D. J. & Gilmore, R. Cotranslational and posttranslational N-glycosylation of polypeptides by distinct mammalian OST isoforms. Cell 136, 272–283 (2009).

    CAS  PubMed  PubMed Central  Google Scholar 

  8. 8

    Helenius, J. et al. Translocation of lipid-linked oligosaccharides across the ER membrane requires Rft1 protein. Nature 415, 447–450 (2002).

    CAS  PubMed  Google Scholar 

  9. 9

    Breitling, J. & Aebi, M. N-linked protein glycosylation in the endoplasmic reticulum. Cold Spring Harb. Perspect. Biol. 5, a013359 (2013).

    PubMed  PubMed Central  Google Scholar 

  10. 10

    Aebi, M. N-linked protein glycosylation in the ER. Biochim. Biophys. Acta 1833, 2430–2437 (2013).

    CAS  PubMed  Google Scholar 

  11. 11

    Takeuchi, H. & Haltiwanger, R. S. Significance of glycosylation in Notch signaling. Biochem. Biophys. Res. Commun. 453, 235–242 (2014).

    CAS  PubMed  PubMed Central  Google Scholar 

  12. 12

    Sentandreu, R. & Northcote, D. H. The structure of a glycopeptide isolated from the yeast cell wall. Biochem. J. 109, 419–432 (1968).

    CAS  PubMed  PubMed Central  Google Scholar 

  13. 13

    Marriott, M. & Tanner, W. Localization of dolichyl phosphate- and pyrophosphate-dependent glycosyl transfer reactions in Saccharomyces cerevisiae. J. Bacteriol. 139, 566–572 (1979).

    CAS  PubMed  PubMed Central  Google Scholar 

  14. 14

    Haselbeck, A. & Tanner, W. O-glycosylation in Saccharomyces cerevisiae is initiated at the endoplasmic reticulum. FEBS Lett. 158, 335–338 (1983).

    CAS  PubMed  Google Scholar 

  15. 15

    Maeda, Y. & Kinoshita, T. Dolichol-phosphate mannose synthase: structure, function and regulation. Biochim. Biophys. Acta 1780, 861–868 (2008).

    CAS  PubMed  Google Scholar 

  16. 16

    Strahl-Bolsinger, S., Immervoll, T., Deutzmann, R. & Tanner, W. PMT1, the gene for a key enzyme of protein O-glycosylation in Saccharomyces cerevisiae. Proc. Natl Acad. Sci. USA 90, 8164–8168 (1993).

    CAS  PubMed  Google Scholar 

  17. 17

    Strahl-Bolsinger, S. & Tanner, W. Protein O-glycosylation in Saccharomyces cerevisiae. Purification and characterization of the dolichyl-phosphate-d-mannose-protein O-d-mannosyltransferase. Eur. J. Biochem. 196, 185–190 (1991).

    CAS  PubMed  Google Scholar 

  18. 18

    Praissman, J. L. & Wells, L. Mammalian O-mannosylation pathway: glycan structures, enzymes, and protein substrates. Biochemistry 53, 3066–3078 (2014).

    CAS  PubMed  PubMed Central  Google Scholar 

  19. 19

    Loibl, M. & Strahl, S. Protein O-mannosylation: what we have learned from baker's yeast. Biochim. Biophys. Acta 1833, 2438–2446 (2013).

    CAS  PubMed  Google Scholar 

  20. 20

    Girrbach, V. & Strahl, S. Members of the evolutionarily conserved PMT family of protein O-mannosyltransferases form distinct protein complexes among themselves. J. Biol. Chem. 278, 12554–12562 (2003).

    CAS  PubMed  Google Scholar 

  21. 21

    Girrbach, V., Zeller, T., Priesmeier, M. & Strahl-Bolsinger, S. Structure-function analysis of the dolichyl phosphate-mannose: protein O-mannosyltransferase ScPmt1p. J. Biol. Chem. 275, 19288–19296 (2000).

    CAS  PubMed  Google Scholar 

  22. 22

    Willer, T., Amselgruber, W., Deutzmann, R. & Strahl, S. Characterization of POMT2, a novel member of the PMT protein O-mannosyltransferase family specifically localized to the acrosome of mammalian spermatids. Glycobiology 12, 771–783 (2002).

    CAS  PubMed  PubMed Central  Google Scholar 

  23. 23

    Gentzsch, M., Immervoll, T. & Tanner, W. Protein O-glycosylation in Saccharomyces cerevisiae: the protein O-mannosyltransferases Pmt1p and Pmt2p function as heterodimer. FEBS Lett. 377, 128–130 (1995).

    CAS  PubMed  Google Scholar 

  24. 24

    Akasaka-Manya, K., Manya, H., Nakajima, A., Kawakita, M. & Endo, T. Physical and functional association of human protein O-mannosyltransferases 1 and 2. J. Biol. Chem. 281, 19339–19345 (2006).

    CAS  PubMed  Google Scholar 

  25. 25

    Rubenstein, E. M., Kreft, S. G., Greenblatt, W., Swanson, R. & Hochstrasser, M. Aberrant substrate engagement of the ER translocon triggers degradation by the Hrd1 ubiquitin ligase. J. Cell Biol. 197, 761–773 (2012).

    CAS  PubMed  PubMed Central  Google Scholar 

  26. 26

    Harty, C., Strahl, S. & Romisch, K. O-mannosylation protects mutant alpha-factor precursor from endoplasmic reticulum-associated degradation. Mol. Biol. Cell 12, 1093–1101 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  27. 27

    Vashist, S. et al. Distinct retrieval and retention mechanisms are required for the quality control of endoplasmic reticulum protein folding. J. Cell Biol. 155, 355–368 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  28. 28

    Nakatsukasa, K. et al. Roles of O-mannosylation of aberrant proteins in reduction of the load for endoplasmic reticulum chaperones in yeast. J. Biol. Chem. 279, 49762–49772 (2004).

    CAS  PubMed  Google Scholar 

  29. 29

    Li, S., Spooner, R. A., Hampton, R. Y., Lord, J. M. & Roberts, L. M. Cytosolic entry of Shiga-like toxin A chain from the yeast endoplasmic reticulum requires catalytically active Hrd1p. PLoS ONE 7, e41119 (2012).

    CAS  PubMed  PubMed Central  Google Scholar 

  30. 30

    Hirayama, H., Fujita, M., Yoko-o, T. & Jigami, Y. O-mannosylation is required for degradation of the endoplasmic reticulum-associated degradation substrate Gas1*p via the ubiquitin/proteasome pathway in Saccharomyces cerevisiae. J. Biochem. 143, 555–567 (2008).

    CAS  PubMed  Google Scholar 

  31. 31

    Coughlan, C. M., Walker, J. L., Cochran, J. C., Wittrup, K. D. & Brodsky, J. L. Degradation of mutated bovine pancreatic trypsin inhibitor in the yeast vacuole suggests post-endoplasmic reticulum protein quality control. J. Biol. Chem. 279, 15289–15297 (2004).

    CAS  PubMed  Google Scholar 

  32. 32

    Duttler, S., Pechmann, S. & Frydman, J. Principles of cotranslational ubiquitination and quality control at the ribosome. Mol. Cell 50, 379–393 (2013).

    CAS  PubMed  Google Scholar 

  33. 33

    Ruggiano, A., Foresti, O. & Carvalho, P. Quality control: ER-associated degradation: protein quality control and beyond. J. Cell Biol. 204, 869–879 (2014).

    CAS  PubMed  PubMed Central  Google Scholar 

  34. 34

    Nakatsukasa, K., Kamura, T. & Brodsky, J. L. Recent technical developments in the study of ER-associated degradation. Curr. Opin. Cell Biol. 29, 82–91 (2014).

    CAS  PubMed  Google Scholar 

  35. 35

    Christianson, J. C. & Ye, Y. Cleaning up in the endoplasmic reticulum: ubiquitin in charge. Nat. Struct. Mol. Biol. 21, 325–335 (2014).

    CAS  PubMed  Google Scholar 

  36. 36

    Olzmann, J. A., Kopito, R. R. & Christianson, J. C. The mammalian endoplasmic reticulum-associated degradation system. Cold Spring Harb. Perspect. Biol. 5, a013185 (2013).

    PubMed  PubMed Central  Google Scholar 

  37. 37

    Thibault, G. & Ng, D. T. The endoplasmic reticulum-associated degradation pathways of budding yeast. Cold Spring Harb. Perspect. Biol. 4, a013193 (2012).

    PubMed  PubMed Central  Google Scholar 

  38. 38

    Finger, A., Knop, M. & Wolf, D. H. Analysis of two mutated vacuolar proteins reveals a degradation pathway in the endoplasmic reticulum or a related compartment of yeast. Eur. J. Biochem. 218, 565–574 (1993).

    CAS  PubMed  Google Scholar 

  39. 39

    McCracken, A. A. & Brodsky, J. L. Assembly of ER-associated protein degradation in vitro: dependence on cytosol, calnexin, and ATP. J. Cell Biol. 132, 291–298 (1996).

    CAS  PubMed  Google Scholar 

  40. 40

    Sommer, T. & Jentsch, S. A protein translocation defect linked to ubiquitin conjugation at the endoplasmic reticulum. Nature 365, 176–179 (1993).

    CAS  PubMed  Google Scholar 

  41. 41

    Carvalho, P., Goder, V. & Rapoport, T. A. Distinct ubiquitin-ligase complexes define convergent pathways for the degradation of ER proteins. Cell 126, 361–373 (2006).

    CAS  Google Scholar 

  42. 42

    Vashist, S. & Ng, D. T. Misfolded proteins are sorted by a sequential checkpoint mechanism of ER quality control. J. Cell Biol. 165, 41–52 (2004).

    CAS  PubMed  PubMed Central  Google Scholar 

  43. 43

    Nakatsukasa, K., Huyer, G., Michaelis, S. & Brodsky, J. L. Dissecting the ER-associated degradation of a misfolded polytopic membrane protein. Cell 132, 101–112 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  44. 44

    Habeck, G., Ebner, F. A., Shimada-Kreft, H. & Kreft, S. G. The yeast ERAD-C ubiquitin ligase Doa10 recognizes an intramembrane degron. J. Cell Biol. 209, 261–273 (2015).

    CAS  PubMed  PubMed Central  Google Scholar 

  45. 45

    Machamer, C. E. & Rose, J. K. Vesicular stomatitis virus G proteins with altered glycosylation sites display temperature-sensitive intracellular transport and are subject to aberrant intermolecular disulfide bonding. J. Biol. Chem. 263, 5955–5960 (1988).

    CAS  PubMed  Google Scholar 

  46. 46

    Gallagher, P., Henneberry, J., Wilson, I., Sambrook, J. & Gething, M. J. Addition of carbohydrate side chains at novel sites on influenza virus hemagglutinin can modulate the folding, transport, and activity of the molecule. J. Cell Biol. 107, 2059–2073 (1988).

    CAS  PubMed  Google Scholar 

  47. 47

    Rutkevich, L. A. & Williams, D. B. Participation of lectin chaperones and thiol oxidoreductases in protein folding within the endoplasmic reticulum. Curr. Opin. Cell Biol. 23, 157–166 (2011).

    CAS  PubMed  Google Scholar 

  48. 48

    Schrag, J. D., Procopio, D. O., Cygler, M., Thomas, D. Y. & Bergeron, J. J. Lectin control of protein folding and sorting in the secretory pathway. Trends Biochem. Sci. 28, 49–57 (2003).

    CAS  PubMed  Google Scholar 

  49. 49

    Caramelo, J. J. & Parodi, A. J. Getting in and out from calnexin/calreticulin cycles. J. Biol. Chem. 283, 10221–10225 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  50. 50

    Ou, W. J., Cameron, P. H., Thomas, D. Y. & Bergeron, J. J. Association of folding intermediates of glycoproteins with calnexin during protein maturation. Nature 364, 771–776 (1993).

    CAS  PubMed  Google Scholar 

  51. 51

    Jackson, M. R., Cohen-Doyle, M. F., Peterson, P. A. & Williams, D. B. Regulation of MHC class I transport by the molecular chaperone, calnexin (p88, IP90). Science 263, 384–387 (1994).

    CAS  PubMed  Google Scholar 

  52. 52

    Hammond, C., Braakman, I. & Helenius, A. Role of N-linked oligosaccharide recognition, glucose trimming, and calnexin in glycoprotein folding and quality control. Proc. Natl Acad. Sci. USA 91, 913–917 (1994).

    CAS  PubMed  Google Scholar 

  53. 53

    Schrag, J. D. et al. The structure of calnexin, an ER chaperone involved in quality control of protein folding. Mol. Cell 8, 633–644 (2001).

    CAS  PubMed  Google Scholar 

  54. 54

    Molinari, M. & Helenius, A. Glycoproteins form mixed disulphides with oxidoreductases during folding in living cells. Nature 402, 90–93 (1999).

    CAS  PubMed  Google Scholar 

  55. 55

    Solda, T., Galli, C., Kaufman, R. J. & Molinari, M. Substrate-specific requirements for UGT1-dependent release from calnexin. Mol. Cell 27, 238–249 (2007).

    CAS  PubMed  Google Scholar 

  56. 56

    Tessier, D. C. et al. Cloning and characterization of mammalian UDP-glucose glycoprotein: glucosyltransferase and the development of a specific substrate for this enzyme. Glycobiology 10, 403–412 (2000).

    CAS  PubMed  Google Scholar 

  57. 57

    Trombetta, E. S. & Helenius, A. Conformational requirements for glycoprotein reglucosylation in the endoplasmic reticulum. J. Cell Biol. 148, 1123–1129 (2000).

    CAS  PubMed  PubMed Central  Google Scholar 

  58. 58

    Ganan, S., Cazzulo, J. J. & Parodi, A. J. A major proportion of N-glycoproteins are transiently glucosylated in the endoplasmic reticulum. Biochemistry 30, 3098–3104 (1991).

    CAS  PubMed  Google Scholar 

  59. 59

    Hitt, R. & Wolf, D. H. DER7, encoding α-glucosidase I is essential for degradation of malfolded glycoproteins of the endoplasmic reticulum. FEMS Yeast Res. 4, 815–820 (2004).

    CAS  PubMed  Google Scholar 

  60. 60

    Camirand, A., Heysen, A., Grondin, B. & Herscovics, A. Glycoprotein biosynthesis in Saccharomyces cerevisiae. Isolation and characterization of the gene encoding a specific processing α-mannosidase. J. Biol. Chem. 266, 15120–15127 (1991).

    CAS  PubMed  Google Scholar 

  61. 61

    Jakob, C. A., Burda, P., Roth, J. & Aebi, M. Degradation of misfolded endoplasmic reticulum glycoproteins in Saccharomyces cerevisiae is determined by a specific oligosaccharide structure. J. Cell Biol. 142, 1223–1233 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  62. 62

    Gauss, R., Kanehara, K., Carvalho, P., Ng, D. T. & Aebi, M. A complex of Pdi1p and the mannosidase Htm1p initiates clearance of unfolded glycoproteins from the endoplasmic reticulum. Mol. Cell 42, 782–793 (2011).

    CAS  PubMed  Google Scholar 

  63. 63

    Dancourt, J. & Barlowe, C. Protein sorting receptors in the early secretory pathway. Annu. Rev. Biochem. 79, 777–802 (2010).

    CAS  PubMed  Google Scholar 

  64. 64

    Jakob, C. A. et al. Htm1p, a mannosidase-like protein, is involved in glycoprotein degradation in yeast. EMBO Rep. 2, 423–430 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  65. 65

    Movsichoff, F., Castro, O. A. & Parodi, A. J. Characterization of Schizosaccharomyces pombe ER α-mannosidase: a reevaluation of the role of the enzyme on ER-associated degradation. Mol. Biol. Cell 16, 4714–4724 (2005).

    CAS  PubMed  PubMed Central  Google Scholar 

  66. 66

    Munro, S. The MRH domain suggests a shared ancestry for the mannose 6-phosphate receptors and other N-glycan-recognising proteins. Curr. Biol. 11, R499–R501 (2001).

    CAS  PubMed  Google Scholar 

  67. 67

    Buschhorn, B. A., Kostova, Z., Medicherla, B. & Wolf, D. H. A genome-wide screen identifies Yos9p as essential for ER-associated degradation of glycoproteins. FEBS Lett. 577, 422–426 (2004).

    CAS  PubMed  Google Scholar 

  68. 68

    Bhamidipati, A., Denic, V., Quan, E. M. & Weissman, J. S. Exploration of the topological requirements of ERAD identifies Yos9p as a lectin sensor of misfolded glycoproteins in the ER lumen. Mol. Cell 19, 741–751 (2005).

    CAS  PubMed  Google Scholar 

  69. 69

    Kim, W., Spear, E. D. & Ng, D. T. Yos9p detects and targets misfolded glycoproteins for ER-associated degradation. Mol. Cell 19, 753–764 (2005).

    CAS  PubMed  Google Scholar 

  70. 70

    Szathmary, R., Bielmann, R., Nita-Lazar, M., Burda, P. & Jakob, C. A. Yos9 protein is essential for degradation of misfolded glycoproteins and may function as lectin in ERAD. Mol. Cell 19, 765–775 (2005).

    CAS  PubMed  Google Scholar 

  71. 71

    Su, Y. A., Hutter, C. M., Trent, J. M. & Meltzer, P. S. Complete sequence analysis of a gene (OS-9) ubiquitously expressed in human tissues and amplified in sarcomas. Mol. Carcinog. 15, 270–275 (1996).

    CAS  PubMed  Google Scholar 

  72. 72

    Quan, E. M. et al. Defining the glycan destruction signal for endoplasmic reticulum-associated degradation. Mol. Cell 32, 870–877 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  73. 73

    Clerc, S. et al. Htm1 protein generates the N-glycan signal for glycoprotein degradation in the endoplasmic reticulum. J. Cell Biol. 184, 159–172 (2009).

    CAS  PubMed  PubMed Central  Google Scholar 

  74. 74

    Knop, M., Hauser, N. & Wolf, D. H. N-Glycosylation affects endoplasmic reticulum degradation of a mutated derivative of carboxypeptidase yscY in yeast. Yeast 12, 1229–1238 (1996).

    CAS  PubMed  Google Scholar 

  75. 75

    Nakatsukasa, K., Nishikawa, S., Hosokawa, N., Nagata, K. & Endo, T. Mnl1p, an α-mannosidase-like protein in yeast Saccharomyces cerevisiae, is required for endoplasmic reticulum-associated degradation of glycoproteins. J. Biol. Chem. 276, 8635–8638 (2001).

    CAS  PubMed  Google Scholar 

  76. 76

    Xie, W., Kanehara, K., Sayeed, A. & Ng, D. T. Intrinsic conformational determinants signal protein misfolding to the Hrd1/Htm1 endoplasmic reticulum-associated degradation system. Mol. Biol. Cell 20, 3317–3329 (2009).

    CAS  PubMed  PubMed Central  Google Scholar 

  77. 77

    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. 284, 11815–11825 (2009).

    CAS  PubMed  PubMed Central  Google Scholar 

  78. 78

    Nishikawa, S. I., Fewell, S. W., Kato, Y., Brodsky, J. L. & Endo, T. Molecular chaperones in the yeast endoplasmic reticulum maintain the solubility of proteins for retrotranslocation and degradation. J. Cell Biol. 153, 1061–1070 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  79. 79

    Buck, T. M., Kolb, A. R., Boyd, C. R., Kleyman, T. R. & Brodsky, J. L. The endoplasmic reticulum-associated degradation of the epithelial sodium channel requires a unique complement of molecular chaperones. Mol. Biol. Cell 21, 1047–1058 (2010).

    CAS  PubMed  PubMed Central  Google Scholar 

  80. 80

    Kabani, M. et al. Dependence of endoplasmic reticulum-associated degradation on the peptide binding domain and concentration of BiP. Mol. Biol. Cell 14, 3437–3448 (2003).

    CAS  PubMed  PubMed Central  Google Scholar 

  81. 81

    Graham, T. R. & Emr, S. D. Compartmental organization of Golgi-specific protein modification and vacuolar protein sorting events defined in a yeast sec18 (NSF) mutant. J. Cell Biol. 114, 207–218 (1991).

    CAS  PubMed  Google Scholar 

  82. 82

    Jungmann, J. & Munro, S. Multi-protein complexes in the cis Golgi of Saccharomyces cerevisiae with α-1,6-mannosyltransferase activity. EMBO J. 17, 423–434 (1998).

    CAS  PubMed  PubMed Central  Google Scholar 

  83. 83

    Hirayama, H., Seino, J., Kitajima, T., Jigami, Y. & Suzuki, T. Free oligosaccharides to monitor glycoprotein endoplasmic reticulum-associated degradation in Saccharomyces cerevisiae. J. Biol. Chem. 285, 12390–12404 (2010).

    CAS  PubMed  PubMed Central  Google Scholar 

  84. 84

    Alonzi, D. S. et al. Glycoprotein misfolding in the endoplasmic reticulum: identification of released oligosaccharides reveals a second ER-associated degradation pathway for Golgi-retrieved proteins. Cell. Mol. Life Sci. 70, 2799–2814 (2013).

    CAS  PubMed  Google Scholar 

  85. 85

    Mueller, B., Klemm, E. J., Spooner, E., Claessen, J. H. & Ploegh, H. L. SEL1L nucleates a protein complex required for dislocation of misfolded glycoproteins. Proc. Natl Acad. Sci. USA 105, 12325–12330 (2008).

    CAS  Google Scholar 

  86. 86

    Christianson, J. C., Shaler, T. A., Tyler, R. E. & Kopito, R. R. OS-9 and GRP94 deliver mutant α1-antitrypsin to the Hrd1–SEL1L ubiquitin ligase complex for ERAD. Nat. Cell Biol. 10, 272–282 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  87. 87

    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. 8, 849–854 (2006).

    CAS  PubMed  Google Scholar 

  88. 88

    Kanehara, K., Xie, W. & Ng, D. T. Modularity of the Hrd1 ERAD complex underlies its diverse client range. J. Cell Biol. 188, 707–716 (2010).

    CAS  PubMed  PubMed Central  Google Scholar 

  89. 89

    Mehnert, M. et al. The interplay of Hrd3 and the molecular chaperone system ensures efficient degradation of malfolded secretory proteins. Mol. Biol. Cell 26, 185–194 (2015).

    PubMed  PubMed Central  Google Scholar 

  90. 90

    Smith, M. H., Rodriguez, E. H. & Weissman, J. S. Misfolded proteins induce aggregation of the lectin Yos9. J. Biol. Chem. 289, 25670–25677 (2014).

    CAS  PubMed  PubMed Central  Google Scholar 

  91. 91

    Benitez, E. M., Stolz, A. & Wolf, D. H. Yos9, a control protein for misfolded glycosylated and non-glycosylated proteins in ERAD. FEBS Lett. 585, 3015–3019 (2011).

    PubMed  Google Scholar 

  92. 92

    Horn, S. C. et al. Usa1 functions as a scaffold of the HRD-ubiquitin ligase. Mol. Cell 36, 782–793 (2009).

    CAS  PubMed  Google Scholar 

  93. 93

    Taxis, C. et al. Use of modular substrates demonstrates mechanistic diversity and reveals differences in chaperone requirement of ERAD. J. Biol. Chem. 278, 35903–35913 (2003).

    CAS  PubMed  Google Scholar 

  94. 94

    Mehnert, M., Sommer, T. & Jarosch, E. Der1 promotes movement of misfolded proteins through the endoplasmic reticulum membrane. Nat. Cell Biol. 16, 77–86 (2014).

    CAS  PubMed  Google Scholar 

  95. 95

    Lilley, B. N. & Ploegh, H. L. A membrane protein required for dislocation of misfolded proteins from the ER. Nature 429, 834–840 (2004).

    CAS  PubMed  Google Scholar 

  96. 96

    Scott, D. C. & Schekman, R. Role of Sec61p in the ER-associated degradation of short-lived transmembrane proteins. J. Cell Biol. 181, 1095–1105 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  97. 97

    Pilon, M., Schekman, R. & Romisch, K. Sec61p mediates export of a misfolded secretory protein from the endoplasmic reticulum to the cytosol for degradation. EMBO J. 16, 4540–4548 (1997).

    CAS  PubMed  PubMed Central  Google Scholar 

  98. 98

    Walter, J., Urban, J., Volkwein, C. & Sommer, T. Sec61p-independent degradation of the tail-anchored ER membrane protein Ubc6p. EMBO J. 20, 3124–3131 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  99. 99

    Schafer, A. & Wolf, D. H. Sec61p is part of the endoplasmic reticulum-associated degradation machinery. EMBO J. 28, 2874–2884 (2009).

    PubMed  PubMed Central  Google Scholar 

  100. 100

    Tretter, T. et al. ERAD and protein import defects in a sec61 mutant lacking ER-lumenal loop 7. BMC Cell Biol. 14, 56 (2013).

    PubMed  PubMed Central  Google Scholar 

  101. 101

    Carvalho, P., Stanley, A. M. & Rapoport, T. A. Retrotranslocation of a misfolded luminal ER protein by the ubiquitin-ligase Hrd1p. Cell 143, 579–591 (2010).

    CAS  PubMed  PubMed Central  Google Scholar 

  102. 102

    Biederer, T., Volkwein, C. & Sommer, T. Role of Cue1p in ubiquitination and degradation at the ER surface. Science 278, 1806–1809 (1997).

    CAS  PubMed  Google Scholar 

  103. 103

    Bays, N. W., Wilhovsky, S. K., Goradia, A., Hodgkiss-Harlow, K. & Hampton, R. Y. HRD4/NPL4 is required for the proteasomal processing of ubiquitinated ER proteins. Mol. Biol. Cell 12, 4114–4128 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  104. 104

    Ye, Y., Meyer, H. H. & Rapoport, T. A. The AAA ATPase Cdc48/p97 and its partners transport proteins from the ER into the cytosol. Nature 414, 652–656 (2001).

    CAS  PubMed  Google Scholar 

  105. 105

    Jarosch, E. et al. Protein dislocation from the ER requires polyubiquitination and the AAA-ATPase Cdc48. Nat. Cell Biol. 4, 134–139 (2002).

    CAS  PubMed  Google Scholar 

  106. 106

    Rabinovich, E., Kerem, A., Fröhlich, K. U., Diamant, N. & Bar-Nun, S. AAA-ATPase p97/Cdc48p, a cytosolic chaperone required for endoplasmic reticulum-associated protein degradation. Mol. Cell. Biol. 22, 626–634 (2002).

    CAS  PubMed  PubMed Central  Google Scholar 

  107. 107

    Stein, A., Ruggiano, A., Carvalho, P. & Rapoport, T. A. Key steps in ERAD of luminal ER proteins reconstituted with purified components. Cell 158, 1375–1388 (2014).

    CAS  PubMed  PubMed Central  Google Scholar 

  108. 108

    Suzuki, T., Park, H., Hollingsworth, N. M., Sternglanz, R. & Lennarz, W. J. PNG1, a yeast gene encoding a highly conserved peptide: N-glycanase. J. Cell Biol. 149, 1039–1052 (2000).

    CAS  PubMed  PubMed Central  Google Scholar 

  109. 109

    Hirsch, C., Blom, D. & Ploegh, H. L. A role for N-glycanase in the cytosolic turnover of glycoproteins. EMBO J. 22, 1036–1046 (2003).

    CAS  PubMed  PubMed Central  Google Scholar 

  110. 110

    Hirsch, C., Misaghi, S., Blom, D., Pacold, M. E. & Ploegh, H. L. Yeast N-glycanase distinguishes between native and non-native glycoproteins. EMBO Rep. 5, 201–206 (2004).

    CAS  PubMed  PubMed Central  Google Scholar 

  111. 111

    Garza, R. M., Sato, B. K. & Hampton, R. Y. In vitro analysis of Hrd1p-mediated retrotranslocation of its multispanning membrane substrate 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase. J. Biol. Chem. 284, 14710–14722 (2009).

    CAS  PubMed  PubMed Central  Google Scholar 

  112. 112

    Medicherla, B., Kostova, Z., Schaefer, A. & Wolf, D. H. A genomic screen identifies Dsk2p and Rad23p as essential components of ER-associated degradation. EMBO Rep. 5, 692–697 (2004).

    CAS  PubMed  PubMed Central  Google Scholar 

  113. 113

    Funakoshi, M., Sasaki, T., Nishimoto, T. & Kobayashi, H. Budding yeast Dsk2p is a polyubiquitin-binding protein that can interact with the proteasome. Proc. Natl Acad. Sci. USA 99, 745–750 (2002).

    CAS  PubMed  Google Scholar 

  114. 114

    Elsasser, S. et al. Proteasome subunit Rpn1 binds ubiquitin-like protein domains. Nat. Cell Biol. 4, 725–730 (2002).

    CAS  PubMed  Google Scholar 

  115. 115

    Li, Y. et al. Rad4 regulates protein turnover at a postubiquitylation step. Mol. Biol. Cell 21, 177–185 (2009).

    CAS  PubMed  Google Scholar 

  116. 116

    Ahner, A., Nakatsukasa, K., Zhang, H., Frizzell, R. A. & Brodsky, J. L. Small heat-shock proteins select ΔF508-CFTR for endoplasmic reticulum-associated degradation. Mol. Biol. Cell 18, 806–814 (2007).

    CAS  PubMed  PubMed Central  Google Scholar 

  117. 117

    Gonzalez, D. S., Karaveg, K., Vandersall-Nairn, A. S., Lal, A. & Moremen, K. W. Identification, expression, and characterization of a cDNA encoding human endoplasmic reticulum mannosidase I, the enzyme that catalyzes the first mannose trimming step in mammalian Asn-linked oligosaccharide biosynthesis. J. Biol. Chem. 274, 21375–21386 (1999).

    CAS  PubMed  Google Scholar 

  118. 118

    Avezov, E., Frenkel, Z., Ehrlich, M., Herscovics, A. & Lederkremer, G. Z. Endoplasmic reticulum (ER) mannosidase I is compartmentalized and required for N-glycan trimming to Man5–6 GlcNAc2 in glycoprotein ER-associated degradation. Mol. Biol. Cell 19, 216–225 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  119. 119

    Roth, J., Brada, D., Lackie, P. M., Schweden, J. & Bause, E. Oligosaccharide trimming Man9-mannosidase is a resident ER protein and exhibits a more restricted and local distribution than glucosidase II. Eur. J. Cell Biol. 53, 131–141 (1990).

    CAS  PubMed  Google Scholar 

  120. 120

    Pan, S., Cheng, X. & Sifers, R. N. Golgi-situated endoplasmic reticulum α-1,2-mannosidase contributes to the retrieval of ERAD substrates through a direct interaction with γ-COP. Mol. Biol. Cell 24, 1111–1121 (2013).

    CAS  PubMed  PubMed Central  Google Scholar 

  121. 121

    Pan, S. et al. Golgi localization of ERManI defines spatial separation of the mammalian glycoprotein quality control system. Mol. Biol. Cell 22, 2810–2822 (2011).

    CAS  PubMed  PubMed Central  Google Scholar 

  122. 122

    Benyair, R. et al. Mammalian ER mannosidase I resides in quality control vesicles, where it encounters its glycoprotein substrates. Mol. Biol. Cell 26, 172–184 (2015).

    PubMed  PubMed Central  Google Scholar 

  123. 123

    Hosokawa, N. et al. A novel ER α-mannosidase-like protein accelerates ER-associated degradation. EMBO Rep. 2, 415–422 (2001).

    CAS  PubMed  PubMed Central  Google Scholar 

  124. 124

    Tamura, T., Cormier, J. H. & Hebert, D. N. Characterization of early EDEM1 protein maturation events and their functional implications. J. Biol. Chem. 286, 24906–24915 (2011).

    CAS  PubMed  PubMed Central  Google Scholar 

  125. 125

    Molinari, M., Calanca, V., Galli, C., Lucca, P. & Paganetti, P. Role of EDEM in the release of misfolded glycoproteins from the calnexin cycle. Science 299, 1397–1400 (2003).

    CAS  PubMed  Google Scholar 

  126. 126

    Oda, Y., Hosokawa, N., Wada, I. & Nagata, K. EDEM as an acceptor of terminally misfolded glycoproteins released from calnexin. Science 299, 1394–1397 (2003).

    CAS  PubMed  Google Scholar 

  127. 127

    Shenkman, M. et al. A shared endoplasmic reticulum-associated degradation pathway involving the EDEM1 protein for glycosylated and nonglycosylated proteins. J. Biol. Chem. 288, 2167–2178 (2013).

    CAS  PubMed  Google Scholar 

  128. 128

    Tang, H. Y., Huang, C. H., Zhuang, Y. H., Christianson, J. C. & Chen, X. EDEM2 and OS-9 are required for ER-associated degradation of non-glycosylated sonic hedgehog. PLoS ONE 9, e92164 (2014).

    PubMed  PubMed Central  Google Scholar 

  129. 129

    Ushioda, R. et al. ERdj5 is required as a disulfide reductase for degradation of misfolded proteins in the ER. Science 321, 569–572 (2008).

    CAS  PubMed  Google Scholar 

  130. 130

    Hosokawa, N. et al. EDEM1 accelerates the trimming of α1,2-linked mannose on the C branch of N-glycans. Glycobiology 20, 567–575 (2010).

    CAS  PubMed  Google Scholar 

  131. 131

    Olivari, S., Galli, C., Alanen, H., Ruddock, L. & Molinari, M. A novel stress-induced EDEM variant regulating endoplasmic reticulum-associated glycoprotein degradation. J. Biol. Chem. 280, 2424–2428 (2005).

    CAS  PubMed  Google Scholar 

  132. 132

    Mast, S. W. et al. Human EDEM2, a novel homolog of family 47 glycosidases, is involved in ER-associated degradation of glycoproteins. Glycobiology 15, 421–436 (2005).

    CAS  PubMed  Google Scholar 

  133. 133

    Hirao, K. et al. EDEM3, a soluble EDEM homolog, enhances glycoprotein endoplasmic reticulum-associated degradation and mannose trimming. J. Biol. Chem. 281, 9650–9658 (2006).

    CAS  PubMed  Google Scholar 

  134. 134

    Ninagawa, S. et al. EDEM2 initiates mammalian glycoprotein ERAD by catalyzing the first mannose trimming step. J. Cell Biol. 206, 347–356 (2014).

    CAS  PubMed  PubMed Central  Google Scholar 

  135. 135

    Hosokawa, N., Kamiya, Y., Kamiya, D., Kato, K. & Nagata, K. Human OS-9, a lectin required for glycoprotein endoplasmic reticulum-associated degradation, recognizes mannose-trimmed N-glycans. J. Biol. Chem. 284, 17061–17068 (2009).

    CAS  PubMed  PubMed Central  Google Scholar 

  136. 136

    Bernasconi, R., Pertel, T., Luban, J. & Molinari, M. A dual task for the Xbp1-responsive OS-9 variants in the mammalian endoplasmic reticulum: inhibiting secretion of misfolded protein conformers and enhancing their disposal. J. Biol. Chem. 283, 16446–16454 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  137. 137

    Hosokawa, N. et al. Human XTP3-B forms an endoplasmic reticulum quality control scaffold with the HRD1–SEL1L ubiquitin ligase complex and BiP. J. Biol. Chem. 283, 20914–20924 (2008).

    CAS  PubMed  PubMed Central  Google Scholar 

  138. 138

    Fujimori, T., Kamiya, Y., Nagata, K., Kato, K. & Hosokawa, N. Endoplasmic reticulum lectin XTP3-B inhibits endoplasmic reticulum-associated degradation of a misfolded α1-antitrypsin variant. FEBS J. 280, 1563–1575 (2013).

    CAS  PubMed  Google Scholar 

  139. 139

    Tyler, R. E. et al. Unassembled CD147 is an endogenous endoplasmic reticulum-associated degradation substrate. Mol. Biol. Cell 23, 4668–4678 (2012).

    CAS  PubMed  PubMed Central  Google Scholar 

  140. 140

    Dersh, D., Jones, S. M., Eletto, D., Christianson, J. C. & Argon, Y. OS-9 facilitates turnover of nonnative GRP94 marked by hyperglycosylation. Mol. Biol. Cell 25, 2220–2234 (2014).

    PubMed  PubMed Central  Google Scholar 

  141. 141

    Bernasconi, R., Galli, C., Calanca, V., Nakajima, T. & Molinari, M. Stringent requirement for HRD1, SEL1L, and OS-9/XTP3-B for disposal of ERAD-LS substrates. J. Cell Biol. 188, 223–235 (2010).

    CAS  PubMed  PubMed Central  Google Scholar 

  142. 142

    Alcock, F. & Swanton, E. Mammalian OS-9 is upregulated in response to endoplasmic reticulum stress and facilitates ubiquitination of misfolded glycoproteins. J. Mol. Biol. 385, 1032–1042 (2009).

    CAS  PubMed  Google Scholar 

  143. 143

    Mikami, K. et al. The sugar-binding ability of human OS-9 and its involvement in ER-associated degradation. Glycobiology 20, 310–321 (2010).

    CAS  PubMed  Google Scholar 

  144. 144

    Satoh, T. et al. Structural basis for oligosaccharide recognition of misfolded glycoproteins by OS-9 in ER-associated degradation. Mol. Cell 40, 905–916 (2010).

    CAS  PubMed  Google Scholar 

  145. 145

    Travers, K. J. et al. Functional and genomic analyses reveal an essential coordination between the unfolded protein response and ER-associated degradation. Cell 101, 249–258 (2000).

    CAS  PubMed  Google Scholar 

  146. 146

    Goder, V. & Melero, A. Protein O-mannosyltransferases participate in ER protein quality control. J. Cell Sci. 124, 144–153 (2011).

    CAS  PubMed  Google Scholar 

  147. 147

    Chalfie, M., Tu, Y., Euskirchen, G., Ward, W. W. & Prasher, D. C. Green fluorescent protein as a marker for gene expression. Science 263, 802–805 (1994).

    CAS  Google Scholar 

  148. 148

    Aronson, D. E., Costantini, L. M. & Snapp, E. L. Superfolder GFP is fluorescent in oxidizing environments when targeted via the Sec translocon. Traffic 12, 543–548 (2011).

    CAS  PubMed  PubMed Central  Google Scholar 

  149. 149

    Xu, C., Wang, S., Thibault, G. & Ng, D. T. Futile protein folding cycles in the ER are terminated by the unfolded protein O-mannosylation pathway. Science 340, 978–981 (2013).

    CAS  PubMed  Google Scholar 

  150. 150

    Denic, V., Quan, E. M. & Weissman, J. S. A luminal surveillance complex that selects misfolded glycoproteins for ER-associated degradation. Cell 126, 349–359 (2006).

    CAS  PubMed  PubMed Central  Google Scholar 

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The authors wish to express their sincere apologies to those researchers whose work is not cited owing to the scope of the review and space constraints, and thank Kun Yang for assistance in rendering figures. Work in the authors' laboratories is supported by funds from the Temasek Trust.

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Correspondence to Davis T. W. Ng.

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HRD1 complex

Multi-subunit membrane protein complex in the endoplasmic reticulum (ER) that is organized around the E3 ubiquitin ligase HMG-CoA reductase degradation 1 (Hrd1). The HRD1 complex receives, retrotranslocates and ubiquitylates substrates for degradation by ER-associated degradation (ERAD).


Member of a class of proteins that bind to carbohydrates. Lectins usually have high specificity for sugar type and/or glycan-linkage configuration.


Member of a class of enzymes that mediate the transfer of electrons from one molecule to another. In the endoplasmic reticulum, most oxidoreductases form and break disulfide bonds.


Particles composed of proteins and lipids, which are usually reconstituted from purified components.

DnaJ protein

A protein containing a 'J domain', which interacts with Hsp70 chaperones and stimulates their ATPase activity. Many DnaJ proteins are chaperones and directly bind to substrates.

Unfolded protein response

(UPR). A signalling response that is triggered by the accumulation of misfolded or unfolded proteins in the endoplasmic reticulum.


Vesicles that are formed from endoplasmic reticulum membranes after mechanical cell disruption.

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Xu, C., Ng, D. Glycosylation-directed quality control of protein folding. Nat Rev Mol Cell Biol 16, 742–752 (2015).

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