| Aspect | Key points | Key evidence/citations | Source details |
|---|---|---|---|
| Identity/synonyms | Verified target is **Saccharomyces cerevisiae PDI1** (UniProt **P17967**), encoding the major ER **protein disulfide-isomerase** (**Pdi1p/Trg1p**); essential gene in budding yeast and distinct from non-yeast PDI1 symbols. | Essentiality and yeast-specific identity established in primary genetics and functional studies (pqac-00000008, pqac-00000011, pqac-00000012) | Nørgaard 2001, *J Cell Biol*, doi:10.1083/jcb.152.3.553, https://doi.org/10.1083/jcb.152.3.553 (Feb 2001); Xiao 2004, *J Biol Chem*, doi:10.1074/jbc.m409210200, https://doi.org/10.1074/jbc.m409210200 (Nov 2004); Young 2013, *Traffic*, doi:10.1111/tra.12041, https://doi.org/10.1111/tra.12041 (Apr 2013) |
| Localization/retention | Pdi1p is a **soluble ER luminal resident**; C-terminal retrieval sequence reported as **AIHDEL** in a yeast ER-resident survey, consistent with classic yeast **HDEL**-mediated retrieval/cycling between ER and Golgi. | ER luminal residency and AIHDEL/HDEL retrieval evidence (pqac-00000012); early yeast gene structure paper identified HDEL retention signal (pqac-00000009) | Young 2013, *Traffic*, doi:10.1111/tra.12041, https://doi.org/10.1111/tra.12041 (Apr 2013); Vala 2008 thesis/lit. summary citing Tachikawa/Farquhar/LaMantia studies (pqac-00000009) |
| Domain architecture & motifs | Canonical multidomain PDI architecture **a-b-b’-a’** plus acidic tail; catalytic domains carry **CGHC/CXXC** motifs, and yeast-specific summaries describe **two WCGHC active sites**. The protein belongs to the thioredoxin-fold/PDI family. | Domain arrangement and CGHC motifs in yeast-specific work (pqac-00000010, pqac-00000011); broader conserved PDI structural context (pqac-00000000, pqac-00000003) | Vitu 2010, *J Biol Chem*, doi:10.1074/jbc.m109.064931, https://doi.org/10.1074/jbc.m109.064931 (Jun 2010); Xiao 2004, *J Biol Chem*, doi:10.1074/jbc.m409210200, https://doi.org/10.1074/jbc.m409210200 (Nov 2004); Melo 2024, *Antioxid Redox Signal*, doi:10.1089/ars.2023.0288, https://doi.org/10.1089/ars.2023.0288 (Aug 2024) |
| Enzymatic activities & mechanism | Primary biochemical function is **disulfide bond formation/isomerization** in secretory proteins (EC **5.3.4.1**). Pdi1p can act as **oxidase**, **reductase**, and **isomerase** depending on active-site redox state; mixed-disulfide intermediates transfer oxidizing equivalents from Pdi1p to client proteins, while reduced Pdi1p resolves/rearranges incorrect disulfides. | Yeast PDI introduces disulfides and rearranges incorrect ones (pqac-00000011); mixed-disulfide catalytic mechanism and domain cooperation from PDI literature (pqac-00000003, pqac-00000000) | Xiao 2004, *J Biol Chem*, doi:10.1074/jbc.m409210200, https://doi.org/10.1074/jbc.m409210200 (Nov 2004); Oliveira 2025, *Biochemistry*, doi:10.1021/acs.biochem.5c00527, https://doi.org/10.1021/acs.biochem.5c00527 (Dec 2025); Melo 2024, *Antioxid Redox Signal*, doi:10.1089/ars.2023.0288, https://doi.org/10.1089/ars.2023.0288 (Aug 2024) |
| Pathway partners | Core oxidative-folding partner is **Ero1p**, which oxidizes Pdi1p; the **N-terminal a domain** of Pdi1p is the preferred route for oxidation of the ER thiol pool. Other PDI-family homologs (**Mpd1, Mpd2, Eug1, Eps1**) are nonessential and only partly substitute; **Mpd1p** is the strongest backup. | Ero1→Pdi1 redox pathway and N-domain preference (pqac-00000010, pqac-00000016); homolog functional differences and rescue hierarchy (pqac-00000008, pqac-00000013) | Vitu 2010, *J Biol Chem*, doi:10.1074/jbc.m109.064931, https://doi.org/10.1074/jbc.m109.064931 (Jun 2010); Nørgaard 2001, *J Cell Biol*, doi:10.1083/jcb.152.3.553, https://doi.org/10.1083/jcb.152.3.553 (Feb 2001); Xiao 2004, *J Biol Chem*, doi:10.1074/jbc.m409210200, https://doi.org/10.1074/jbc.m409210200 (Nov 2004) |
| ERQC/ERAD roles | Beyond oxidative folding, Pdi1p contributes to **ER quality control** by rearranging/unscrambling non-native disulfides and participating in client triage. Yeast mutant analyses found CPY folding and glycan-processing defects when PDI family functions are compromised. In newer work, Pdi1 partners with **Htm1/Mnl1** in glycoprotein ERAD, where the complex can switch Pdi1 from oxidative folding toward **disulfide reduction** of misfolded glycoproteins. | “Unscrambling” non-native disulfides and QC evidence (pqac-00000004, pqac-00000008, pqac-00000011); recent ERAD model with Htm1/Mnl1-Pdi1 complex (pqac-00000017) | Laboissière 1995, *J Biol Chem*, doi:10.1074/jbc.270.47.28006, https://doi.org/10.1074/jbc.270.47.28006 (Nov 1995); Nørgaard 2001, *J Cell Biol*, doi:10.1083/jcb.152.3.553, https://doi.org/10.1083/jcb.152.3.553 (Feb 2001); Zhao 2025, *Nat Struct Mol Biol*, doi:10.1038/s41594-025-01491-y, https://doi.org/10.1038/s41594-025-01491-y (Feb 2025) |
| Quantitative data | In vivo, yeast Pdi1p active sites are **~32 ± 8% reduced** (about **1.3 ± 0.3** free sulfhydryls per molecule; **n=11**), indicating a partially reduced steady state that supports both oxidation and isomerization. Pdi1p **a domain** is oxidized by Ero1p faster than the **a’** domain and other ER oxidoreductases, establishing a rank preference for flux through the N-terminal active site. | Redox-state numbers from yeast cells (pqac-00000014); oxidation preference/rank order and mixed-disulfide evidence (pqac-00000010, pqac-00000016) | Xiao 2004, *J Biol Chem*, doi:10.1074/jbc.m409210200, https://doi.org/10.1074/jbc.m409210200 (Nov 2004); Vitu 2010, *J Biol Chem*, doi:10.1074/jbc.m109.064931, https://doi.org/10.1074/jbc.m109.064931 (Jun 2010) |
| Applications/biotech evidence | Yeast PDI1 is widely used as a **secretory-pathway engineering target** to improve folding/secretion of recombinant disulfide-bonded proteins. Recent production studies in methylotrophic yeasts still treat PDI/PDI1 as an auxiliary foldase, though gains are often protein-specific and can be overshadowed by broader UPR engineering (e.g., **HAC1**). Comparative context: in **K. phaffii**, **pdi1Δ** strains still secreted disulfide-bonded proteins but at reduced biomass-normalized yields (**~40% of WT** for scFvM; **~27% of WT** for trypsinogen). | PDI/PDI1 as secretion engineering target and UPR component (pqac-00000023); comparative pdi1Δ secretion yields in another yeast (pqac-00000020, pqac-00000024) | De Groeve 2023, *Microb Cell Fact*, doi:10.1186/s12934-023-02132-z, https://doi.org/10.1186/s12934-023-02132-z (Jul 2023); Palma 2024, *bioRxiv*, doi:10.1101/2024.08.21.609038, https://doi.org/10.1101/2024.08.21.609038 (Aug 2024) |
| Recent developments 2023-2024 | Recent literature emphasizes three themes: (1) updated mechanistic models of PDI redox relays and conformational control; (2) continued use of PDI/PDI1 in yeast strain engineering for heterologous protein production; and (3) new evidence that Pdi1 can be **functionally repurposed in ERAD/reductive quality control**, not only oxidative folding. These developments refine rather than replace the classical view of yeast Pdi1 as the central ER oxidoreductase. | Mechanistic review/update (pqac-00000000); recombinant-production engineering context (pqac-00000023); comparative essentiality/alternative oxidoreductases in yeast (pqac-00000019, pqac-00000022) | Melo 2024, *Antioxid Redox Signal*, doi:10.1089/ars.2023.0288, https://doi.org/10.1089/ars.2023.0288 (Aug 2024); De Groeve 2023, *Microb Cell Fact*, doi:10.1186/s12934-023-02132-z, https://doi.org/10.1186/s12934-023-02132-z (Jul 2023); Palma 2024, *bioRxiv*, doi:10.1101/2024.08.21.609038, https://doi.org/10.1101/2024.08.21.609038 (Aug 2024) |


*Table: This table summarizes verified identity, localization, mechanism, pathway context, quantitative findings, and recent research relevant to Saccharomyces cerevisiae PDI1 (UniProt P17967). It is useful as a compact evidence map for functional annotation and literature-supported interpretation.*