Recombinant Danio rerio Transmembrane protein 47 (tmem47)

What is TMEM47 and what is its biological function in zebrafish?

Zebrafish Transmembrane protein 47 (TMEM47) functions as a negative regulator of interferon (IFN) production during viral infections. Research has demonstrated that TMEM47 acts as a brake to inhibit IFN production in both RNA and DNA viral infections . The protein is also known by the aliases tm4sf10 and zgc:63990, and is sometimes referred to as Transmembrane 4 superfamily member 10 .

TMEM47 plays a critical role in maintaining homeostasis of cellular IFN responses by targeting key adaptor proteins in innate immune signaling pathways. Its expression is rapidly upregulated during viral infection, suggesting a negative feedback mechanism to prevent excessive inflammatory responses that could harm the host .

How is recombinant Danio rerio TMEM47 typically produced for research purposes?

Recombinant Danio rerio TMEM47 is typically produced using the following approach:

• Expression system: In vitro E. coli expression system is commonly employed

• Protein format: Full-length protein (amino acids 1-181) is expressed

• Affinity tag: An N-terminal 10xHis-tag is frequently added to facilitate purification

• Purification: Affinity chromatography utilizing the His-tag followed by additional purification steps

• Final format: Provided either as liquid or lyophilized powder, often in Tris/PBS-based buffer with 6% Trehalose, pH 8.0

This production method allows researchers to obtain purified TMEM47 protein for various experimental applications, including in vitro binding assays, antibody production, and functional studies.

What are the optimal storage and handling conditions for recombinant TMEM47?

To maintain the stability and activity of recombinant TMEM47, researchers should follow these guidelines:

• Storage conditions:

  • Store at -20°C/-80°C upon receipt

  • Aliquot for multiple uses to avoid repeated freeze-thaw cycles

  • Liquid form has approximately 6 months shelf life at -20°C/-80°C

  • Lyophilized form has approximately 12 months shelf life at -20°C/-80°C

• Working solutions:

  • Store working aliquots at 4°C for up to one week

  • Avoid repeated freezing and thawing

• Reconstitution:

  • When reconstituting lyophilized protein, use sterile techniques and the recommended buffer

  • Allow complete dissolution before use

Proper storage and handling are critical for maintaining protein functionality, particularly for transmembrane proteins like TMEM47 that may be prone to aggregation or loss of native conformation.

What methodological approaches are recommended for confirming the identity and purity of recombinant TMEM47?

For confirming the identity and purity of recombinant TMEM47, researchers should employ multiple complementary techniques:

• SDS-PAGE: To assess protein purity and approximate molecular weight (expected 23-25 kDa)

• Western blot: Using anti-His antibodies or specific anti-TMEM47 antibodies to confirm protein identity

• Mass spectrometry: For precise molecular mass determination and sequence verification

• Circular dichroism: To evaluate secondary structure and proper folding

• Size exclusion chromatography: To assess oligomeric state and detect potential aggregation

These analyses should be performed routinely when working with new batches of recombinant TMEM47 to ensure consistent experimental results.

What is the mechanism by which TMEM47 regulates interferon production during viral infections?

TMEM47 employs a sophisticated regulatory mechanism to control interferon production through the following molecular events:

• TMEM47 interacts directly with both MAVS and STING, which are key adaptor proteins in RNA and DNA virus sensing pathways, respectively

• These interactions promote the degradation of MAVS and STING through an autophagy-lysosome-dependent mechanism

• The autophagy factor ATG5 is essential for this TMEM47-mediated degradation process

• TMEM47 localizes to the endoplasmic reticulum, positioning it strategically to interact with components of innate immune signaling pathways

• Through this degradation process, TMEM47 attenuates MAVS- and STING-mediated signaling, ultimately reducing IFN production

Experimental evidence supporting this mechanism includes:

• Overexpression of TMEM47 significantly blocks SVCV- and CyHV-2-mediated IFN induction

• Knockdown of tmem47 promotes ifn transcription during viral infections

• Both MAVS- and STING-mediated antiviral capacities are significantly suppressed by TMEM47

This regulatory circuit represents a negative feedback mechanism to prevent excessive immune activation that could lead to immunopathology.

How can researchers effectively investigate TMEM47-MAVS and TMEM47-STING interactions?

To investigate the interactions between TMEM47 and its binding partners (MAVS and STING), researchers should employ multiple complementary techniques:

• Co-immunoprecipitation (Co-IP):

  • TMEM47 was originally identified as a TBK1-associated protein through Co-IP screening

  • Use tagged versions of proteins (e.g., His-tagged TMEM47 ) for specific pull-down

  • Include appropriate controls to verify specificity of interactions

• Proximity-based assays:

  • Proximity Ligation Assay (PLA) for visualizing interactions in situ

  • Bimolecular Fluorescence Complementation (BiFC) for monitoring interactions in live cells

  • Förster Resonance Energy Transfer (FRET) for quantitative assessment of protein proximities

• Domain mapping:

  • Generate truncation mutants to identify specific interaction domains

  • Perform site-directed mutagenesis of conserved residues to determine critical interaction sites

  • Use peptide competition assays to confirm binding interfaces

• Subcellular localization studies:

  • Perform confocal microscopy to visualize colocalization of TMEM47 with MAVS and STING

  • Consider the ER localization of TMEM47 when designing experiments

  • Use organelle-specific markers to confirm sites of interaction

These methodological approaches will provide comprehensive insights into the spatial, temporal, and molecular details of TMEM47's interactions with key components of innate immune signaling pathways.

What experimental approaches should be used to study the autophagy-lysosome-dependent degradation pathway mediated by TMEM47?

To investigate the autophagy-lysosome-dependent degradation pathway through which TMEM47 mediates the degradation of MAVS and STING, researchers should implement the following experimental approaches:

• Pharmacological interventions:

  • Use autophagy inhibitors (3-methyladenine, wortmannin) and lysosomal inhibitors (bafilomycin A1, chloroquine)

  • Monitor effects on MAVS/STING stability in presence of TMEM47

  • Quantify protein levels by western blotting with appropriate controls

• Genetic manipulation of autophagy components:

  • Generate ATG5 knockout or knockdown cells, as ATG5 is essential for TMEM47-mediated degradation

  • Use CRISPR-Cas9 or RNAi approaches for targeted manipulation

  • Include rescue experiments by re-expressing the targeted genes

• Imaging approaches:

  • Monitor colocalization of TMEM47, MAVS/STING with autophagosomal (LC3) and lysosomal (LAMP1) markers

  • Perform time-lapse imaging to capture dynamic degradation processes

  • Use tandem fluorescent-tagged LC3 (mRFP-GFP-LC3) to distinguish early autophagosomes from autolysosomes

• Biochemical analyses:

  • Assess ubiquitination status of MAVS/STING in response to TMEM47 expression

  • Monitor LC3 lipidation (LC3-I to LC3-II conversion) as a marker of autophagy induction

  • Examine p62/SQSTM1 levels as an indicator of autophagic flux

• Flow cytometry:

  • Quantify autophagic vesicles using specific dyes (e.g., Cyto-ID)

  • Measure lysosomal activity using LysoTracker or LysoSensor probes

  • Analyze large cell populations for statistical robustness

These approaches will provide mechanistic insights into how TMEM47 directs MAVS and STING to autophagic degradation, with particular attention to the essential role of ATG5 in this process.

How do various viral infections affect TMEM47 expression and function?

Understanding the dynamic regulation of TMEM47 during viral infections is crucial for elucidating its role in immune homeostasis:

• Temporal expression patterns:

  • The mRNA level of tmem47 is rapidly upregulated during both RNA virus (SVCV) and DNA virus (CyHV-2) infections

  • Expression increases after infection for 24 hours and reaches a peak at 48 hours

  • This pattern is observed in multiple zebrafish cell lines, including ZF4 and ZFL cells

• Correlation with antiviral gene expression:

  • The upregulation of tmem47 occurs alongside increases in key antiviral genes including ifnφ1 and irf7

  • This suggests TMEM47 functions as part of a coordinated antiviral response program

• Functional consequences:

  • Overexpression of TMEM47 significantly blocks both SVCV- and CyHV-2-mediated IFN induction

  • Knockdown of tmem47 promotes ifn transcription under these viral infections

  • TMEM47 targets both RNA (MAVS) and DNA (STING) virus sensing pathways, providing broad regulatory capacity

These findings suggest that TMEM47 plays a critical role in a negative feedback loop that prevents excessive IFN production during both RNA and DNA viral infections, helping to maintain immune homeostasis while allowing effective antiviral responses.

What are the challenges in designing functional assays for recombinant TMEM47 activity?

Researchers face several challenges when designing functional assays for recombinant TMEM47 due to its unique properties as a membrane protein and immune regulator:

• Protein solubility and stability issues:

  • As a transmembrane protein, TMEM47 may require specific buffer conditions

  • Detergents may be necessary to maintain solubility but might affect function

  • Optimization of pH, salt concentration, and stabilizing agents is critical

• Reconstituting physiological membrane environment:

  • Function may depend on proper membrane integration

  • Consider using liposomes, nanodiscs, or detergent micelles to mimic native environment

  • Evaluate different lipid compositions to optimize activity

• Assessing degradation-promoting activity:

  • Design cell-free systems to measure TMEM47-mediated degradation of MAVS/STING

  • Include purified components of autophagy machinery, including ATG5

  • Monitor degradation kinetics under controlled conditions

• Detecting protein-protein interactions:

  • Recombinant TMEM47 with N-terminal 10xHis-tag may require optimization for interaction studies

  • Consider tag interference with binding partners

  • Use multiple binding assays to confirm interactions (ELISA, SPR, ITC)

• Maintaining physiological relevance:

  • Compare activity of recombinant protein to endogenous TMEM47

  • Validate findings in cellular systems

  • Consider post-translational modifications that may be absent in E. coli-expressed protein

By addressing these challenges through careful experimental design and validation, researchers can develop robust functional assays for recombinant TMEM47 that provide meaningful insights into its biological activities.

How can researchers resolve contradictions in TMEM47 research data?

When confronting contradictory findings in TMEM47 research, researchers should employ systematic approaches to resolve discrepancies:

• Methodological differences analysis:

  • Compare experimental conditions across studies (cell types, protein tags, expression levels)

  • Assess whether recombinant TMEM47 production methods differ (E. coli vs. eukaryotic expression)

  • Evaluate whether the full-length protein (amino acids 1-181) or truncated versions were used

• Context-dependent functionality:

  • Investigate whether TMEM47 function varies depending on:

    • Viral infection type (RNA vs. DNA viruses)

    • Cell type (ZF4 vs. ZFL vs. other systems)

    • Experimental timepoints (expression peaks at 48h post-infection)

  • Design experiments that directly compare conditions within the same system

• Isoform and post-translational modification analysis:

  • Determine if multiple isoforms exist with distinct functions

  • Assess whether post-translational modifications affect activity

  • Compare results from different expression systems that may result in different modifications

• Interaction partner variability:

  • Investigate whether TMEM47 interactions with MAVS, STING, and ATG5 are influenced by experimental conditions

  • Consider whether additional, unidentified interaction partners modulate activity

  • Develop comprehensive interaction networks to contextualize findings

• Standardization approaches:

  • Develop reference standards for TMEM47 activity

  • Establish common assay protocols across laboratories

  • Create shared resources (antibodies, cell lines, recombinant proteins)

By systematically addressing these potential sources of contradiction, researchers can develop a more coherent understanding of TMEM47 biology and its role in regulating innate immune responses.

What comparative analyses can be performed between zebrafish TMEM47 and its homologs in other species?

Comparative analysis of TMEM47 across species provides valuable insights into evolutionary conservation and functional divergence:

• Sequence-based comparisons:

  • Zebrafish TMEM47 shows homology to proteins in other bony fish species with high scores (202-343)

  • Homologs in primitive fish, chordates, and invertebrates (including bivalves) show moderate similarity (scores 53.5-162)

  • Bacterial TenA proteins display lower but significant sequence similarity (scores 60.8-90.5)

• Structure-function relationships:

  • Compare conserved domains across species to identify critical functional regions

  • Analyze transmembrane topology predictions across homologs

  • Identify conserved motifs that may mediate interactions with MAVS, STING, and ATG5

• Experimental functional comparisons:

  • Express TMEM47 homologs from different species in zebrafish cells

  • Assess their ability to regulate IFN production during viral infection

  • Determine whether they interact with zebrafish MAVS and STING

• Evolutionary analysis:

  • Construct phylogenetic trees to trace the evolutionary history of TMEM47

  • Identify patterns of positive selection that may indicate functional adaptation

  • Correlate evolutionary changes with differences in immune system organization

• Conservation of regulatory mechanisms:

  • Compare expression patterns of TMEM47 homologs during viral infections across species

  • Assess whether the autophagy-lysosome-dependent degradation mechanism is conserved

  • Determine if the requirement for ATG5 is maintained across species

These comparative approaches will provide insights into the evolutionary conservation of TMEM47 function and may reveal species-specific adaptations in immune regulation that could inform therapeutic strategies for modulating immune responses.