Table 2.
Box 2 Workers in the secretory protein factory (an incomplete list)
| (A) ‘Public' chaperones and enzymes | |||
|---|---|---|---|
| Class | Name | Localization | Function |
| Chaperones | BiP/GRP78 | ER | Folding assistant/unfolding Regulation of IRE1, PERK and ATF6 in ER signaling Translocon gating and regulation |
| GRP94 | ER | Folding assistant | |
| ORP150 | ER | Folding assistant, hypoxia | |
| HERP | ER membrane | ERAD | |
| SEL1L | ER membrane | ERAD | |
| Co-chaperones | Sil1/BAP ERdjs | ER ER | ATP exchange factor BiP cofactors |
| Lectins | CNX | ER membrane | Folding |
| CRT | ER soluble | Folding | |
| ERGIC-53 | ERGIC | Transport F5, F8, CatZ, CatC, IgM polymers | |
| VIPL | ER | Transport | |
| VIP-36 | Cis-Golgi | Transport | |
| EDEM1, 2, 3 | ER subregion | ERAD | |
| OS9 | ER membrane | ERAD | |
| Erlectin/XTP3-B | ER membrane | ERAD | |
| Enzymes redox | Ero1α | ER+ERGIC | Oxidase |
| Ero1β | ER | Oxidase | |
| PDI | ER | Oxidase, isomerase, reductase Subunit of prolyl 4-hydroxylase Subunit of microsomal triacylglycerol transfer protein | |
| ERp57 | ER | Isomerase, oxidase? | |
| ERp72 | ER | Unclear | |
| ERp44 | ERGIC-cis-Golgi | Thiol-mediated retention/IP3R1 regulation | |
| Proline isomerases | PPIases Cyclophilins | ER ER, mitochondria, nucleus, cytosol | Proline isomerization |
| Proline isomerization | |||
| Sugar processing | Glucosidase I | ER | |
| Glucosidase II | ER | ||
| ER Man I | ER | ||
| ER Man II | ER | ||
| UGGT | ER | Folding sensor | |
| Man IA, IB, IC | Golgi | ||
| (B) ‘Private' tissue- or substrate-specific factors | |||
| Name |
Tissue expression |
Substrates/function |
|
| Hsp47 | Fibroblasts | Collagen biosynthesis/chaperone | |
| PDIp | Exocrine pancreas | Zymogens/oxidoreductase | |
| PDILT | Sertoli cells in testis | Calmegin, Δ-somatostatin/ chaperone | |
| Egasyn | Ubiquitous | β-Glucuronidase/chaperone | |
| Invariant chain | APC | MHC class II assembly and transport | |
| Tapasin | Ubiquitous | MHC class I assembly | |
| SCAP-RAP Boca/Mesd | Ubiquitous | LDL receptor assembly and transport | |
| APC, antigen-presenting cell; CNX, calnexin; CRT, calreticulin; ER Man, ER α1,2-mannosidase; ER, endoplasmic reticulum; ERAD, ER-associated degradation; ERGIC, ER–Golgi intermediate compartment; LDL, low-density lipoprotein; MHC, major histocompatibility complex; UGGT, UDP-glucose glycoprotein glucosyltransferase. | |||