TXNRD1 Human
Description
Protein Structure
TXNRD1 is a homodimeric flavoenzyme with a molecular weight of 55.7 kDa (508 amino acids) and a selenocysteine (Sec) residue at its active site, which is essential for catalytic activity . The protein includes:
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FAD cofactor: Facilitates electron transfer from NADPH to thioredoxin (Trx) .
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Selenocysteine insertion: Encoded by a UGA codon via the SECIS element in the 3' UTR, ensuring proper translation .
Table 1: TXNRD1 Isoforms and Their Features
Recombinant Protein Production
TXNRD1 is commonly expressed in E. coli as a non-glycosylated protein with:
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Tagging: N-terminal His-tag or Myc-DDK-tag for purification .
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Activity: Measured via DTNB/NADPH assays (e.g., >15 units/mg) .
Core Biological Functions
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Thioredoxin Reduction: TXNRD1 reduces oxidized Trx1, enabling the latter to regenerate glutathione and repair oxidized proteins .
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Oxidative Stress Mitigation: Protects cells from reactive oxygen species (ROS) by reducing hydrogen peroxide (H₂O₂) .
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Selenium Metabolism: The Sec residue is critical for its catalytic activity and selenium incorporation .
Regulatory Mechanisms
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Elovanoid-N34 Interaction: Modulates TXNRD1 activity by altering FAD and dimer interface domains, particularly under oxidative stress .
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Protein-Protein Interactions: Isoforms 2, 3, or 5 interact with lipid mediators like ELV-N34, influencing redox signaling .
Cancer and TXNRD1
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Hepatocellular Carcinoma (HCC): TXNRD1 is upregulated in HCC tumors and correlates with poor survival. Knockdown reduces proliferation and metastasis, while overexpression activates Akt/mTOR signaling via PTEN degradation .
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Therapeutic Target: Silencing TXNRD1 inhibits tumor growth in xenograft models, suggesting its role in oncogenesis .
Genetic Variants and Aging
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SNP Associations: Variants like rs4445711 and rs7310505 correlate with physical performance and longevity in elderly populations. These SNPs influence redox homeostasis and survival post-85 years .
Table 3: Genetic Variants and Their Associations
| SNP | Associated Trait | Population | Significance (p-value) | Reference |
|---|---|---|---|---|
| rs4445711 | Reduced chair stand performance | Southern Italians | p < 0.022 | |
| rs7310505 | Walking ability, longevity | Northern Europeans | p < 0.072 |
Neuroprotection and Oxidative Stress
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ELV-N34 Modulation: This lipid mediator binds TXNRD1 isoforms 2/3/5, reducing cytosolic/membrane-bound activity and mitigating uncompensated oxidative stress (UOS) .
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Ferroptosis Resistance: TXNRD1 structural changes under UOS enhance ELV-N34 interaction, highlighting its role in neuroprotection .
Molecular Biology Tools
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ORF Clones: Available for transcript variant 4 (NM_182743) with Myc-DDK or GFP tags, enabling studies on selenocysteine incorporation .
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Bioactivity Assays: DTNB-based assays quantify TXNRD1’s reductase activity, critical for validating recombinant protein quality .
Tissue Expression
TXNRD1 is ubiquitously expressed, with high levels in:
Product Specs
Thioredoxin reductase 1 cytoplasmic, TR, GRIM-12, Gene associated with retinoic and IFN-induced mortality 12 protein, KM-102-derived reductase-like factor, Thioredoxin reductase TR1, TXNRD1, GRIM12, KDRF, TR1, TXNR, TRXR1, MGC9145.
MGSSHHHHHH SSGLVPRGSH MYDYDLIIIG GGSGGLAAAK EAAQYGKKVM VLDFVTPTPL GTRWGLGGTC VNVGCIPKKL MHQAALLGQALQDSRNYGWK VEETVKHDWD RMIEAVQNHI GSLNWGYRVA LREKKVVYEN AYGQFIGPHR IKATNNKGKE KIYSAERFLI ATGERPRYLGIPGDKEYCIS SDDLFSLPYC PGKTLVVGAS YVALECAGFL AGIGLDVTVM VRSILLRGFD QDMANKIGEH MEEHGIKFIR QFVPIKVEQIEAGTPGRLRV VAQSTNSEEI IEGEYNTVML AIGRDACTRK IGLETVGVKI NEKTGKIPVT DEEQTNVPYI YAIGDILEDK VELTPVAIQAGRLLAQRLYA GSTVKCDYEN VPTTVFTPLE YGACGLSEEK AVEKFGEENI EVYHSYFWPL EWTIPSRDNN KCYAKIICNT KDNERVVGFH VLGPNAGEVT QGFAAALKCG LTKKQLDSTI GIHPVCAEVF TTLSVTKRSG ASILQAGC.
Q&A
What is the basic structure and function of human TXNRD1?
TXNRD1 is a selenoprotein containing a redox-active selenocysteine residue that displays broad substrate specificity. It functions as part of the thioredoxin system, which includes thioredoxin (TXN), thioredoxin reductase (TXNRD), and NADPH. This system participates in various cellular reactions and is found across all organisms . TXNRD1 is primarily cytosolic, distinguishing it from other mammalian TXNRD isoenzymes: mitochondrial TXNRD2 and testis-prevalent TGR .
The thioredoxin system plays pivotal roles in:
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Antioxidant defense
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Growth promotion
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Neuroprotection
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Inflammatory modulation
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Antiapoptosis
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Immune function
How is TXNRD1 genomically organized and what splice variants exist?
TXNRD1 is located on chromosome 12 (NC_000012.12 in the GRCh38.p14 reference assembly) . The gene has a complex organization with multiple splice variants. Research has identified:
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At least 20 different splice variants
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Three separate promoters
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Five different open reading frames
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Novel variants including a glutaredoxin motif
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Alternative N-terminal domains with potential mitochondrial targeting signal peptides
The most common 5'-UTR variant has been characterized with promoter activity maintained within the -115 to +167 region across multiple cell lines .
What is the tissue-specific expression pattern of TXNRD1?
TXNRD1 expression varies significantly across human tissues. Northern blot analyses have revealed:
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Highest mRNA levels: Liver and kidney
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Lowest mRNA levels: Testis
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Highly structured expression in kidney: Prominently synthesized in the proximal tubules of the medullary rays
Advanced in situ hybridization studies have demonstrated this highly organized expression pattern, suggesting tissue-specific roles for this enzyme.
How do genetic variants in TXNRD1 influence age-related conditions and longevity?
Genetic variability in TXNRD1 has been associated with age-related physiological decline and longevity. Key findings include:
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Three variants (rs4445711, rs1128446, and rs11111979) are associated with physical functioning after 85 years of age (p < 0.022)
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Two SNPs (rs4964728 and rs7310505) show borderline influence on longevity
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rs7310505 associates with both health status and survival in Northern Europeans
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TXNRD1 variants correlate with Activity of Daily Living (ADL), differentiating successfully aged individuals from those with disabilities
These findings establish TXNRD1 as a potential biomarker for healthy aging and longevity.
What is the role of TXNRD1 in cancer progression and metastasis?
TXNRD1 has significant implications in cancer biology, particularly in breast cancer. A comprehensive meta-analysis of 13,322 breast cancer patients from 43 independent cohorts revealed:
Quantitatively, patients with high TXNRD1 expression experience:
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2.5 years earlier recurrence
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1.3 years earlier metastasis compared to patients with low TXNRD1 expression
TXNRD1 is also overexpressed in multiple other cancers, including cholangiocarcinoma, colon adenocarcinoma, esophageal carcinoma, and various lung cancers .
How does TXNRD1 modulate response to cancer therapeutics?
TXNRD1 expression significantly influences therapeutic outcomes:
These findings position TXNRD1 as a potential predictor for therapy response in cancer treatment planning.
What evidence supports TXNRD1's role in neurodegenerative diseases?
TXNRD1 has been implicated in neuroprotection against age-related neurodegenerative conditions:
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Associated with neuroprotection against Alzheimer's and Parkinson's diseases
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Upregulation of TXNRD1 has been suggested as a strategy for prevention and treatment of these age-related neurodegenerative diseases
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Functions as part of the "vitagenes" (genes involved in preserving cellular homeostasis under stress), together with heat shock proteins and sirtuin systems
What are the optimal approaches for studying TXNRD1 genetic variants?
When investigating TXNRD1 variants, researchers have employed these methodological approaches:
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Tagging SNP selection: Prioritize SNPs by functional relevance (nonsynonymous SNPs, SNPs in 5' and 3' UTR regions)
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Minor allele frequency (MAF) threshold: Exclude SNPs with MAF < 5%
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Linkage disequilibrium analysis: Assess LD between pairs of SNPs (r² < 0.8 indicates independent analysis needed)
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Statistical testing: Apply RobustSNP algorithm based on score tests, suitable for both quantitative and binary traits
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Age stratification: Divide samples (e.g., into long-lived subjects >85 years and younger controls ≤85 years)
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Multiple genetic models: Test dominant, recessive, and additive models
What techniques are effective for analyzing TXNRD1 expression patterns?
Multiple complementary techniques have proven valuable:
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Northern blot analysis for tissue-specific expression profiling
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In situ hybridization for detailed spatial expression patterns
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5'RACE PCR combined with bioinformatic tools for identifying alternative transcripts
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Luciferase reporter vectors for promoter activity assessment
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Deletion constructs to identify minimal promoter regions (e.g., -115 to +167 region)
For cancer research specifically, data mining approaches using:
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METABRIC database via cBioPortal
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TCGA RNA-seq data via UCSC Xena platform
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CPTAC protein expression data
How should researchers determine optimal cut-off points when analyzing TXNRD1 expression data?
When analyzing TXNRD1 as a biomarker, researchers should consider multiple methods for determining expression cut-offs:
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Data-driven approaches for maximum significance between chosen arms (high vs. low)
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Outcome-oriented methods (generally superior to data-oriented methods)
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Cut-off finder web applications specifically designed for molecular data
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Statistical methods including:
These approaches allow for rigorous stratification of patient populations based on TXNRD1 expression levels.
How does TXNRD1 interact with the Nrf2 pathway in oxidative stress response?
TXNRD1 has a complex relationship with the Nrf2 (Nuclear factor erythroid 2-related factor 2) pathway:
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TXNRD1 is regulated by Nrf2, a master regulator of antioxidant responses
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During oxidative stress, TXNRD1 and Nrf2 form part of a feedback loop
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In cancer contexts, elevated ROS generation observed in TXNRD1-high cells suggests an altered redox balance
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The interaction has implications for radiation sensitivity and chemotherapeutic responses
Future research should explore the mechanistic details of this relationship and potential therapeutic interventions targeting this pathway.
What are the contradictory findings regarding TXNRD1 in therapeutic response?
TXNRD1 demonstrates seemingly paradoxical effects on therapeutic outcomes:
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High TXNRD1 correlates with better response to neoadjuvant chemotherapy (pathologic complete response)
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Yet high TXNRD1 also associates with earlier recurrence after radiotherapy
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TXNRD1 depletion enhances sensitivity to radiation-induced killing
These contradictions suggest context-dependent functions that warrant detailed mechanistic investigation to resolve these apparent discrepancies.
How do mitochondrial and cytosolic thioredoxin systems coordinate in cellular redox homeostasis?
While TXNRD1 is primarily cytosolic, evidence suggests complex coordination with mitochondrial TXNRD2:
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Alternative splice variants of TXNRD1 may include mitochondrial targeting signals
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Compartmentalization of redox systems creates distinct redox environments
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Cross-talk between cytosolic and mitochondrial thioredoxin systems may occur during stress
Research employing subcellular fraction analyses, live-cell imaging, and compartment-specific redox sensors would help elucidate these complex interactions.
Product Science Overview
Thioredoxin Reductase 1 is a homodimeric enzyme, meaning it consists of two identical subunits. Each subunit contains a flavin adenine dinucleotide (FAD) prosthetic group and a selenocysteine residue at the active site. The enzyme catalyzes the reduction of thioredoxin, a small redox protein, using NADPH as an electron donor. The reaction can be summarized as follows:
This reduction process is essential for various cellular processes, including DNA synthesis, repair, and defense against oxidative stress .
Thioredoxin Reductase 1 is involved in several critical biological functions:
- Redox Regulation: It helps maintain the redox balance within cells by reducing oxidized thioredoxin, which in turn reduces other proteins through cysteine thiol-disulfide exchange.
- Antioxidant Defense: By reducing thioredoxin, TXNRD1 indirectly contributes to the detoxification of reactive oxygen species (ROS), protecting cells from oxidative damage.
- Cell Growth and Survival: The enzyme is involved in regulating cell proliferation and apoptosis. It has been shown to influence the activity of various transcription factors and signaling pathways.
- Selenium Metabolism: As a selenoprotein, TXNRD1 plays a role in selenium metabolism, which is vital for the proper function of several other selenoproteins .
Recombinant Human Thioredoxin Reductase 1 is produced using Escherichia coli (E. coli) expression systems. The recombinant protein typically includes an N-terminal His-tag to facilitate purification. The amino acid sequence of the recombinant protein corresponds to the amino acids 161-647 of the native human enzyme .
The recombinant form retains the enzymatic activity of the native protein, making it useful for various research applications, including studies on redox biology, drug development, and understanding the enzyme’s role in disease processes .
Recombinant Thioredoxin Reductase 1 is widely used in biochemical and biomedical research. Some of its applications include:
- Studying Redox Mechanisms: Researchers use the recombinant enzyme to investigate the mechanisms of redox regulation and the role of thioredoxin in cellular processes.
- Drug Screening: The enzyme is used in high-throughput screening assays to identify potential inhibitors or activators that could be developed into therapeutic agents.
- Disease Research: Given its involvement in cancer, cardiovascular diseases, and neurodegenerative disorders, TXNRD1 is a target of interest in understanding the molecular basis of these diseases and developing targeted therapies .
