| Claim/Finding | Evidence type (biochemical/genetic/transcriptional/review) | Quantitative details | Source (first author year, journal) | URL/DOI |
|---|---|---|---|---|
| **Identity and architecture of A. niger tigA/TIGA (UniProt Q00216) match an ER PDI-family protein** | Genetic/sequence | ORF encodes **359 aa** precursor (~**38.7 kDa**), predicted signal peptide cleavage between **aa 19–20**, mature protein **340 aa**; two **CGHC** active-site motifs at **aa 49–52** and **169–172**; C-terminal **KDEL** ER-retention signal; transcript ~**1.35 kb**; single-copy gene (pqac-00000005, pqac-00000007, pqac-00000013) | Jeenes 1997, *Gene*; Liang 2005, *Biochemistry and Cell Biology* | https://doi.org/10.1016/S0378-1119(97)00098-X ; https://doi.org/10.1139/O05-117 |
| **Domain organization is atypical relative to canonical PDI** | Sequence/biochemical | TIGA contains two thioredoxin-like domains (**a0** and **a**) plus a helical **ERp29c-like D domain**; lacks the redox-inactive **b/b'** domains of canonical PDI and shares only ~**20% sequence identity** with PDI (pqac-00000002, pqac-00000004, pqac-00000014, pqac-00000016) | Liang 2005, *Biochemistry and Cell Biology* | https://doi.org/10.1139/O05-117 |
| **Localization is most consistent with the ER lumen / early secretory pathway** | Genetic/inferential | Evidence includes N-terminal signal peptide plus C-terminal **KDEL**; authors conclude TigA is likely ER-lumenal and may operate at different sites within the **ER-to-cis-Golgi** network than HDEL-bearing PDIA (pqac-00000005, pqac-00000013) | Jeenes 1997, *Gene* | https://doi.org/10.1016/S0378-1119(97)00098-X |
| **TIGA is a bona fide disulfide isomerase/foldase** | Biochemical | Promotes refolding of reduced, denatured **RNase A** in glutathione redox buffer; activity is **~10% of human PDI** under assay conditions (pqac-00000000, pqac-00000002, pqac-00000014, pqac-00000015) | Liang 2005, *Biochemistry and Cell Biology* | https://doi.org/10.1139/O05-117 |
| **Catalysis depends on the two thioredoxin motifs, with unequal contributions** | Biochemical/mutagenesis | Wild type = **100%** activity; **NCCCSS** (only N-terminal motif intact) = **62.6%**; **NSSCCC** (only C-terminal motif intact) = **48.3%**; **NCSCCS** (second cysteines mutated) = **7.4%**; **NSSCSS** and **NSCCSC** = **0%**. Conclusion: N-terminal motif more active; the **first cysteine** in each motif is essential (pqac-00000000, pqac-00000002, pqac-00000015) | Liang 2005, *Biochemistry and Cell Biology* | https://doi.org/10.1139/O05-117 |
| **TIGA has chaperone activity, but it is substrate selective** | Biochemical | In prochymosin refolding, TIGA increased yield from **2% to ~13%** at **1:10 TIGA:prochymosin** molar ratio; inactive mutant **NSSCSS** still improved yield to **4%** at 1:10 and **~17%** at equimolar ratio, indicating a trx-independent chaperone component (pqac-00000000, pqac-00000015) | Liang 2005, *Biochemistry and Cell Biology* | https://doi.org/10.1139/O05-117 |
| **Chaperone function is not universal across substrates** | Biochemical | TIGA promoted refolding of disulfide-containing **prochymosin** but did **not** improve reactivation or suppress aggregation of **GAPDH** (a non-disulfide substrate), unlike canonical PDI; this supports **substrate specificity** (pqac-00000002, pqac-00000004, pqac-00000016) | Liang 2005, *Biochemistry and Cell Biology* | https://doi.org/10.1139/O05-117 |
| **Early interpretation suggested stronger oxidoreductase/oxidase-like than high-isomerase behavior** | Sequence/inference | Jeenes et al. noted the active-site composition suggested a **strongly oxidizing oxidoreductase** and the lack of an acidic peptide-binding region argued against high isomerase activity, consistent with later biochemical observation that TigA is weaker than canonical PDI in RNase refolding (pqac-00000001, pqac-00000013) | Jeenes 1997, *Gene* | https://doi.org/10.1016/S0378-1119(97)00098-X |
| **tigA is ER-stress responsive to tunicamycin** | Transcriptional | **~2–3-fold** mRNA induction after a **~3 h lag** following tunicamycin treatment; promoter contains an **ERPTRE-like** element (~**70%** identity to mammalian ERp72 ERPTRE) and a **grp-core-like** element (~**75%** identity), supporting secretion-stress regulation (pqac-00000001, pqac-00000005, pqac-00000007) | Jeenes 1997, *Gene* | https://doi.org/10.1016/S0378-1119(97)00098-X |
| **tigA is strongly induced by reductive ER stress (DTT)** | Transcriptional | In A. niger AB4.1, **20 mM DTT** increased tigA mRNA **~4-fold at 40 min** and **~8-fold at 2 h**; bipA induction was larger, and tigA transcript abundance was ~**3–4-fold lower** than pdiA at baseline (pqac-00000006, pqac-00000012) | Ngiam 2000, *Applied and Environmental Microbiology* | https://doi.org/10.1128/AEM.66.2.775-782.2000 |
| **tigA responds to Ca2+-homeostasis perturbation (A23187)** | Transcriptional | A23187 caused tigA mRNA to increase **~3.5-fold after 1–2 h** in A. niger; pdiA response was weaker and bipA rose **~6.3-fold** before declining (pqac-00000006, pqac-00000012) | Ngiam 2000, *Applied and Environmental Microbiology* | https://doi.org/10.1128/AEM.66.2.775-782.2000 |
| **tigA is linked to secretion stress and heterologous protein production** | Transcriptional/genetic | In HEWL-overproducing A. niger strains, mRNA levels of **tigA**, **pdiA**, and **bipA** were all higher than in parent strain AB4.1, connecting tigA to secretory load adaptation (pqac-00000006, pqac-00000012) | Ngiam 2000, *Applied and Environmental Microbiology* | https://doi.org/10.1128/AEM.66.2.775-782.2000 |
| **Genome-scale secretion-stress profiling places tigA among induced ER foldases** | Transcriptomics | In A. niger secretion stress/UPR studies, TigA is grouped with lumenal foldases (**PdiA, TigA, PrpA**); all were generally up-regulated by secretion stressors except tigA was not induced in one **DTT** condition in the GeneChip dataset, underscoring stressor-specific regulation (pqac-00000003) | Guillemette 2007, *BMC Genomics* | https://doi.org/10.1186/1471-2164-8-158 |
| **Role in the broader ER oxidative folding pathway is well supported by recent reviews** | Review | Recent fungal secretion reviews place PDI-family proteins in the ER folding network that converts nascent secretory proteins to native form before Golgi trafficking; Fig. 1 in the 2024 review summarizes the ER→Golgi secretory route in filamentous fungi (pqac-00000010, pqac-00000024) | Jadhav 2024, *Applied Microbiology and Biotechnology* | https://doi.org/10.1007/s00253-023-12985-4 |
| **Recent mechanistic work on fungal ERp38/ERp29-like proteins supports TigA-family functional interpretation** | Biochemical/comparative | A 2024 study on **Komagataella phaffii Erp41** describes an ER-resident fungal **ERp38/TigA-type** PDI-family protein with two thioredoxin-like domains plus an **ERp29_C** domain, reinforcing current understanding of TigA-like proteins as specialized ER oxidoreductases rather than canonical PDI equivalents (pqac-00000008, pqac-00000009, pqac-00000011) | Palma 2024, *Journal of Biological Chemistry* | https://doi.org/10.1016/j.jbc.2024.105746 |
| **Industrial relevance: ER folding/redox remains a bottleneck in A. niger protein production** | Review/engineering | A. niger is a major secretion host, but heterologous non-fungal proteins often yield **~three orders of magnitude** less than fungal proteins; one 2023 monellin study achieved only **0.284 mg/L** in shake flasks after multi-pronged engineering, illustrating persistent ER/secretion bottlenecks (pqac-00000019, pqac-00000020) | Li 2023, *Journal of Fungi* | https://doi.org/10.3390/jof9050528 |
| **Industrial relevance: helper folding pathways are directly engineered in A. niger** | Engineering | The monellin study explicitly tested overexpression of **pdiA** and **bipA**, ERAD attenuation (**ΔhrdC**), copy-number increase, protease deletion, and membrane engineering; although TigA was not directly manipulated, the work shows PDI-family folding helpers remain central engineering targets (pqac-00000018, pqac-00000020, pqac-00000022) | Li 2023, *Journal of Fungi* | https://doi.org/10.3390/jof9050528 |
| **Industrial relevance: redox engineering can improve secretion without directly editing tigA** | Engineering | In 2024 A. niger, **Glr1** overexpression reduced intracellular ROS by **50%**, increased glucoamylase activity by **243%**, and increased total protein secretion by **88%**; authors explicitly link ROS generation to ER oxidative folding by **PDI/ERO**, highlighting the pathway context in which TigA likely acts (pqac-00000017) | Chen 2024, *Biotechnology for Biofuels and Bioproducts* | https://doi.org/10.1186/s13068-024-02542-0 |


*Table: This table compiles the main evidence for Aspergillus niger tigA/TIGA, including protein architecture, ER localization, biochemical activity, stress regulation, and relevance to secretion engineering. It is useful as a quick-reference map from primary experiments and recent reviews to the specific claims made about this protein.*