Glycoprotein Maturation and Quality Control in the Endoplasmic Reticulum Department of Biochemistry and Molecular Biology University of Massachusetts, USA 1 Intracellular protein trafficking Plasma membrane Melanosome Golgi complex Lysosome/ Vacuole Mitochondrion Endoplasmic reticulum mra Peroxisome ucleus 2 Protein maturation in the secretory pathway Co-translational translocation Protein folding Co- and post-translational modifications Assembly Quality control Retention Unfolding Disaggregation Degradation Transport 3 The screen versions of these slides have full details of copyright and acknowledgements 1
Signal Sequence Signal recognition particle SRP receptor Cis Translocon Trans Schnell & Hebert (2003) Cell 112: 491 4 Folding & assembly Quality control Misfolding & misassembly Transport Degradation 5 6 The screen versions of these slides have full details of copyright and acknowledgements 2
Glucoses Mannoses -acety l glucosamine GlcAc Asn-X-Ser/Thr Asn C 7 Glucosidase I Glucosidase II Mannosidase Asn-X-Ser/Thr C 8 ER glycoforms 9 The screen versions of these slides have full details of copyright and acknowledgements 3
The glyco-code of the ER Code Foldedness Localization - Age Encoders - Glycosidases - Transferases Decoders - Lectin chaperones - Quality control and trafficking receptors 10 Calnexin Calreticulin Type I membrane protein 67kD Ca 2+ binder Soluble 54kD Ca 2+ binder KDEL KPRRE 11 P domain Calnexin ERp57 C Carbohydrate Binding domain Modified from J. Schrag et al., (2001) Mol. Cell 8: 633-644 12 The screen versions of these slides have full details of copyright and acknowledgements 4
Helenius et al., (1997) Trends Cell Biol. 7(5): 193-200 13 Calnexin binding cycle CX/CRT ERp57 Glucosidase II G3 G2 G1 G0 G0 Glucosidase I Glucosidase II Glucosidase II Mannosidases I & II GT 14 Calnexin/calreticulin functions Increase the fidelity of protein folding Slow folding Barrier to aggregation, confinement Retain misfolded and unassembled proteins Target proteins for degradation 15 The screen versions of these slides have full details of copyright and acknowledgements 5
Co-translational Co-translational folding folding 16 Average protein synthesis time Prokaryotes (~6 sec) ~300 amino acids Translation rate (~50 aa/sec) Eukaryotes (~2 min) ~500 amino acids Translation rate (5 aa/sec) 17 165 Influenza hemagglutinin 165 81 14 52 67 76 97 8 22 38 81 81 38 139 165 285 285 277 22 281 305 285 38 22 8 483 466 473 477 483 8 483 C 550 18 The screen versions of these slides have full details of copyright and acknowledgements 6
Oxidation of HA 165 Time 81 IT1 IT2 T on-reducing 38 22 285 R Reducing 8 483 C 19 HA truncations -linked glycosylation Signal sequence cleavage Chaperone binding Disulfide bond formation Folding 20 Daniels et al., (2003) Molecular Cell (11) 79-90 21 The screen versions of these slides have full details of copyright and acknowledgements 7
Type I membrane proteins HA 8 38 68 TYR Soluble 211 354 Factor V 22 23 Transport ative ATIVE Unfolded UFOLDED Retain Quality control Aggregate Degrade 24 The screen versions of these slides have full details of copyright and acknowledgements 8
Loss of function vs. gain of toxicity 25 Disease states involving ER folding and quality control Cystic fibrosis Emphysema/liver disease Scurvy Hereditary hyperlipemia Glanzman's thromobostenia Cong. sucrase-isomaltase deficiency Hexosaminidase A deficiency CFTR α -antitrypsin Procollagen LDL-receptor Integrin receptor Sucrase-isomaltase Hexosaminidase Marfan's syndrome Fibrinogen storage disease anomelia (in chicken) α -antichymotrypsin deficiency von Willebrand's disease Retinitis pigmentosa Osteogenesis imperfecta Glioblastoma Aspartylglucoseaminuria Maroteaux-Lamy syndrome Hurler syndrome Albinism Fibrillin Fibrinogen Aggrecan α -antichymotrypsinogen vw factor Rhodopsin Collagens EGF receptor Aspartylglucoseaminidase Lysosomal 4-sulfatase α -L-iduronidase Tyrosinase 26 Tyrosinase is a bona fide ERAD substrate TM C C85S nucleus ER Golgi Melanosomes 27 The screen versions of these slides have full details of copyright and acknowledgements 9
Tyr(C85S) is retained in the ER TYR CX Merge TYR GM130 Merge WT C85S Svedine et al., J. Cell Science 2004 WT TYR TYR(C85S) 28 Functional vs. structural 29 Structural determinants that cause retention Exposed hydrophobic areas Unassembled multimers Free-thiols Aggregation 30 The screen versions of these slides have full details of copyright and acknowledgements 10
ER retention signals KDEL (soluble proteins, BiP, calreticulin, GRP94 etc. HDEL in yeast) KKXX (type I membrane proteins) Calcium matrix 31 Calnexin binding cycle CX/CRT ERp57 Glucosidase II G3 G2 G1 G0 G0 Glucosidase I Glucosidase II Glucosidase II Mannosidases I & II GT 32 GT or UDP-glucose glycoprotein: glucosyltransferase Reglucosylation of substrates by GT involves a two step process: Substrate recognition Glucose transfer GT binds and reglucosylates proteins with: on-native molten globular like structures (Carmelo et al., PAS 2003; Carmelo et al., J. Biol. Chem. 2004) Hydrophobic domains C-terminal to the glycan (Taylor et al., EMBO Rep. 2003) Glycans situated near disulfide bond disruptions (Ritter et al., EMBO J. 2005) GT reglucosylation supports re-entry of substrates into the calnexin cycle and their subsequent retention in the ER 33 The screen versions of these slides have full details of copyright and acknowledgements 11
Degradation of misfolded proteins Recognition/sorting (carbohydrates) Translocation (unfolding) Tagging (ubiquitination) Degradation (proteasome) 34 Carbohydrate trimming is critical for the maturation and quality control of glycoproteins CX/CRT ERp57 Transport Mannosidase Gls II G3 G2 G0 G1 Degradation Gls I Gls II Gls II GT 35 EDEM1, a putative mannose-binding protein C Homologous to ER mannosidase I 36 The screen versions of these slides have full details of copyright and acknowledgements 12
EDEM1 levels influence the degradation of ERAD substrates Protein Half-life (min) Control -EDEM +EDEM Reference A1AT-HK 120 A 60 Hosokawa et al., 2001 EMBO J BACE457 240 >420 30 BACE457 45 120 30 Molinari et al., 2003 Science BACE457 OG 90 A 90 herg-lqt2 192 570 A Gong et al., 2005 JBC Tyr-C85S 180 A 120 Cormier & D..H. unpublished results 37 EDEM1 extracts proteins from the calnexin cycle 38 Hebert et al., (2005) Trends Cell Biol. 15(7):364-370 39 The screen versions of these slides have full details of copyright and acknowledgements 13
40 The screen versions of these slides have full details of copyright and acknowledgements 14