TMX4 Antibody

What is TMX4 and what is its cellular localization pattern?

TMX4 (Thioredoxin-related transmembrane protein 4) is a member of the protein disulfide isomerase (PDI) family located primarily in the endoplasmic reticulum (ER) of mammalian cells. It is a type I transmembrane protein with a distinctive Trx-like domain that faces the ER lumen . Interestingly, TMX4 has been observed to have peculiar enrichment in the nuclear envelope (NE), distinguishing it from other PDI family members .

When conducting immunofluorescence studies, TMX4 typically displays a reticular pattern consistent with ER localization, with notable concentration at the nuclear periphery. This dual localization pattern can be visualized using immunofluorescence with antibodies such as 21348-1-AP, which has been validated in multiple cell lines including HepG2 cells .

What is the molecular structure and key domains of TMX4?

TMX4 possesses a distinctive domain architecture that defines its function:

• An N-terminal ER signal sequence

• A catalytic thioredoxin-like (Trx-like) domain containing a non-canonical CPSC active site motif

• A single transmembrane domain

• A C-terminal cytoplasmic region

The non-canonical cysteine-proline-serine-cysteine (CPSC) active site sequence is particularly noteworthy. The proline residue at position 2 destabilizes the disulfide state and favors the di-thiol reduced form of the active site, which contributes to TMX4's function as a reductase . The calculated molecular weight of TMX4 is 39 kDa (349 amino acids), although the observed molecular weight in experimental conditions is typically 40-45 kDa due to post-translational modifications .

How does TMX4 function differ from other thioredoxin family members?

TMX4 exhibits distinct characteristics compared to its paralogs:

TMX4 has a measured redox potential of −171.5 mV (at 30°C, pH 7.0), which enables it to function as a reductase in the ER environment . Unlike TMX3, which captures a different subset of client proteins and primarily catalyzes oxidation of client proteins, TMX4 preferentially interacts with NESPRIN proteins and appears to have specialized functions at the nuclear envelope .

What are the validated applications for TMX4 antibody?

The TMX4 antibody (21348-1-AP) has been validated for multiple experimental applications:

For optimal results in immunohistochemistry applications, antigen retrieval with TE buffer pH 9.0 is recommended, although citrate buffer pH 6.0 may alternatively be used . The antibody has confirmed reactivity with human, mouse, and rat samples, making it versatile for comparative studies across these species.

How should I optimize Western blot protocols for TMX4 detection?

For optimal TMX4 detection in Western blot applications:

• Sample preparation:

  • Extract total protein from cells or tissues using RIPA buffer containing protease inhibitors

  • Determine protein concentration using Bradford or BCA assay

  • Load 20-50 μg of total protein per lane

• Gel electrophoresis:

  • Use 10-12% SDS-PAGE gels for optimal resolution around 40-45 kDa

  • Include positive control samples such as mouse brain tissue or A375 cells

• Transfer and blocking:

  • Transfer proteins to PVDF membrane (preferred over nitrocellulose for this application)

  • Block with 5% non-fat milk in TBST for 1 hour at room temperature

• Antibody incubation:

  • Dilute primary TMX4 antibody (21348-1-AP) at 1:1000 in blocking buffer

  • Incubate overnight at 4°C with gentle agitation

  • Wash 3x with TBST, 5 minutes each

  • Incubate with HRP-conjugated secondary antibody at 1:5000 for 1 hour at room temperature

• Detection:

  • Develop using ECL substrate

  • Observe for bands at 40-45 kDa

Note that different cellular contexts may result in slight variations in the observed molecular weight due to post-translational modifications .

What controls should I include when using TMX4 antibody?

To ensure experimental rigor when using TMX4 antibody:

• Positive controls:

  • Mouse brain tissue lysate

  • A375 cells or HepG2 cells known to express TMX4

  • Cells overexpressing tagged TMX4 (e.g., TMX4-HA) for specificity confirmation

• Negative controls:

  • Samples with TMX4 knockdown using validated siRNAs (e.g., siTMX4-1: 5′-UUUACGCUGCCUCAAGGAGUCUUCC-3′ or siTMX4-2: 5′-UGAUAUUACCACCAAGACCAGACCC-3′)

  • Preincubation of antibody with immunizing peptide to block specific binding

  • Secondary antibody only control to assess non-specific binding

• Loading controls:

  • Standard housekeeping proteins (β-actin, GAPDH)

  • ER-resident protein (calnexin, BiP) for subcellular fraction verification

These controls help validate antibody specificity and ensure reliable interpretation of experimental results.

How can I study TMX4's redox activity in cellular contexts?

To investigate TMX4's redox activity:

• Maleimide alkylation assay:

  • Treat cells with oxidizing agents (e.g., thapsigargin, tunicamycin) or reducing agents (e.g., DTT)

  • Lyse cells in non-reducing buffer containing maleimide

  • Perform Western blot to analyze shifts in TMX4 mobility corresponding to different redox states

  • In normal conditions, most endogenous TMX4 exists in the oxidized form

• Redox potential measurement:

  • Express and purify recombinant TMX4 Trx-like domain (e.g., residues 35-185)

  • Incubate with varying ratios of GSH/GSSG and measure thiol-disulfide exchange

  • Calculate redox potential using the Nernst equation

  • TMX4 has a measured redox potential of −171.5 mV (30°C, pH 7.0)

• Mixed disulfide trapping approach:

  • Generate TMX4 with active site mutation (e.g., TMX4 C67A)

  • Express in cells to trap mixed disulfides with client proteins

  • Immunoprecipitate and analyze trapped complexes by mass spectrometry

  • This approach has identified NESPRIN proteins as major TMX4 clients

What methodologies can be employed to study TMX4-NESPRIN interactions?

To investigate the unique TMX4-NESPRIN interactions:

• Co-immunoprecipitation strategies:

  • Express TMX4 C67A trapping mutant with V5 tag

  • Immunoprecipitate using anti-V5 antibodies

  • Analyze immunocomplexes under non-reducing and reducing conditions

  • Identify interacting partners by silver staining and mass spectrometry

• Mixed disulfide analysis:

  • Co-express TMX4 C67A with NESPRIN3

  • Identify mixed disulfides (~200 kDa) corresponding to TMX4-S-S-NESPRIN3 by immunoblotting

  • Confirm composition by dual immunoreactivity with both anti-NESPRIN3 and anti-V5 antibodies

  • Validate disulfide nature by observing signal collapse under reducing conditions

• Comparative client profiling:

  • Use trapping mutants of different PDI family members (TMX3 C56A, TMX4 C67A, TMX5)

  • Identify unique client subsets through proteomics

  • Compare with published datasets (e.g., TMX1 clients)

  • This approach has demonstrated that NESPRINs are uniquely captured by TMX4 but not by TMX1, TMX3, or TMX5

How can I investigate TMX4's role during ER stress conditions?

To study TMX4's function during ER stress:

• Stress induction and expression analysis:

  • Treat cells with ER stress inducers: thapsigargin (300 nM), tunicamycin (2 μg/ml), or DTT (5 mM) for 6 hours

  • Extract RNA for Northern blotting or qRT-PCR

  • Compare TMX4 expression with established ER stress markers (BiP)

  • Analyze protein levels by Western blotting

• TMX4 knockdown effects during stress:

  • Transfect cells with validated siRNAs targeting TMX4

  • Subject to ER stress conditions

  • Assess impact on unfolded protein response markers

  • Evaluate cell survival and apoptosis rates

• Protein complex analysis:

  • Investigate changes in TMX4's interactions with calnexin and ERp57 during ER stress

  • Perform sequential co-immunoprecipitation experiments

  • Analyze results by Western blot or mass spectrometry to identify stress-dependent dynamic changes in the protein folding complex

Why might I observe multiple bands when detecting TMX4 by Western blot?

Multiple bands in TMX4 Western blots may appear due to:

• Post-translational modifications:

  • The calculated molecular weight of TMX4 is 39 kDa, but observed weight is typically 40-45 kDa

  • Glycosylation or phosphorylation may result in migration shifts

  • Treatment with deglycosylating enzymes can confirm glycosylation status

• Redox state variations:

  • Different redox forms (reduced/oxidized) may migrate differently

  • Mixed disulfide complexes with client proteins may appear as higher molecular weight bands

  • Compare non-reducing versus reducing conditions to distinguish redox-dependent bands

• Proteolytic processing:

  • Sample preparation conditions may affect protein integrity

  • Include protease inhibitors and maintain samples at cold temperatures

  • Avoid freeze-thaw cycles that may lead to degradation

• Non-specific binding:

  • Optimize antibody dilution (recommended range: 1:500-1:2000)

  • Increase blocking time and stringency of wash steps

  • Validate specificity using TMX4 knockdown samples

How can I distinguish between different TMX family members in my experiments?

To differentiate between TMX proteins:

The distinct subcellular distribution of TMX4 with enrichment in the nuclear envelope provides a particularly useful distinguishing feature from other TMX family members .

What factors affect TMX4 antibody sensitivity in different applications?

Several factors influence TMX4 antibody performance:

• Sample preparation:

  • For Western blot: Complete denaturation of samples improves epitope accessibility

  • For IHC: Proper antigen retrieval (recommended: TE buffer pH 9.0) is critical for signal intensity

  • For IF: Fixation method affects epitope preservation (4% paraformaldehyde for 20 min is optimal)

• Antibody dilution:

  • Application-dependent optimal ranges:

    • WB: 1:500-1:2000

    • IHC: 1:20-1:200

    • IF/ICC: 1:20-1:200

  • Titration is recommended for each experimental system

• Detection system:

  • For WB: HRP-conjugated secondary antibodies with ECL substrate

  • For IF: Alexa Fluor-conjugated secondary antibodies provide superior signal-to-noise ratio

  • For IHC: DAB detection system with hematoxylin counterstain

• Expression levels:

  • TMX4 expression varies across tissues and cell types

  • Northern blot analysis can help determine optimal sample types

  • Known positive samples include mouse brain tissue and HepG2 cells

How can I investigate the functional significance of TMX4 in the nuclear envelope?

To explore TMX4's unique nuclear envelope localization:

• High-resolution imaging approaches:

  • Super-resolution microscopy (STORM, PALM)

  • Correlative light and electron microscopy

  • Live-cell imaging with fluorescently tagged TMX4

  • Co-localization with nuclear envelope markers (Lamin B1, nuclear pore components)

• Nuclear envelope fractionation:

  • Isolate nuclear envelope fractions using established protocols

  • Compare TMX4 enrichment relative to other ER and nuclear envelope proteins

  • Analyze protein complexes by blue native PAGE

• CRISPR-based approaches:

  • Generate TMX4 knockout cell lines

  • Assess nuclear envelope morphology and integrity

  • Evaluate impact on nucleocytoplasmic transport

  • Analyze NESPRIN localization and dynamics

• Domain mapping:

  • Create chimeric proteins between TMX4 and other TMX family members

  • Identify domains responsible for nuclear envelope targeting

  • Evaluate functional consequences of mislocalization

How can TMX4's role in protein quality control be systematically investigated?

For comprehensive analysis of TMX4's protein quality control functions:

• Client protein identification:

  • Use substrate-trapping mutants (TMX4 C67A)

  • Perform quantitative proteomics to identify TMX4-dependent substrates

  • Compare client profiles under normal and stress conditions

  • Validate key interactions with co-immunoprecipitation and proximity labeling approaches

• Redox interactome mapping:

  • Employ redox-specific proteomics techniques

  • Use isotope-coded affinity tags to quantify thiol modifications

  • Compare TMX4-dependent redox changes across various cellular compartments

• Functional redundancy analysis:

  • Generate combined knockdowns of multiple PDI family members

  • Assess compensatory mechanisms

  • Identify unique versus overlapping functions between TMX4 and other oxidoreductases

• Disease relevance exploration:

  • Examine TMX4 expression and function in neurological disorders

  • Investigate potential roles in cancer cell models

  • Explore connections to ER stress-related pathologies