Recombinant Xenopus tropicalis Protein FAM134C (fam134c)

What is FAM134C and how does it relate to other FAM134 family proteins?

FAM134C (Family with sequence similarity 134 member C), also known as RETREG3 (Reticulophagy regulator 3), belongs to the FAM134 protein family of reticulon-like proteins involved in ER-phagy, the selective autophagy of endoplasmic reticulum. FAM134C shares high sequence similarity with FAM134B, unlike FAM134A which clearly deviates from this sequence pattern . This sequence conservation suggests functional overlap, particularly regarding membrane binding and remodeling activities. Both FAM134B and FAM134C interact with bacterial lipopolysaccharide (LPS) with similar efficiency as demonstrated in in vitro streptavidin pulldown assays, whereas FAM134A shows significantly weaker interaction . The evolutionary conservation of FAM134C across species makes Xenopus tropicalis FAM134C a valuable model for studying conserved functions of this protein family.

How is recombinant Xenopus tropicalis FAM134C protein typically produced?

Recombinant Xenopus tropicalis FAM134C protein is typically produced through heterologous expression in E. coli expression systems . The production process involves:

• Cloning the full-length cDNA (1-457 amino acids) into an expression vector with an N-terminal His-tag

• Transformation into E. coli expression strains

• Induction of protein expression

• Cell lysis and protein purification using metal affinity chromatography

• Final purification through size-exclusion chromatography to achieve >90% purity as determined by SDS-PAGE

• Lyophilization in Tris/PBS-based buffer containing 6% trehalose at pH 8.0

For experimental use, the lyophilized protein is reconstituted in deionized sterile water to a concentration of 0.1-1.0 mg/mL, with 5-50% glycerol (typically 50%) added for long-term storage stability at -20°C/-80°C .

What experimental approaches can be used to study FAM134C interactions with bacterial components?

Based on the methodologies used to study FAM134B, several experimental approaches can be applied to investigate FAM134C interactions with bacterial components:

• In vitro binding assays:

  • Streptavidin pulldown assays with biotin-labeled LPS: This approach successfully demonstrated that biotin-LPS pulled down FAM134C and FAM134B with similar efficiency

  • Co-immunoprecipitation experiments with tagged FAM134C and bacterial components

• Structural analysis:

  • Blue native PAGE to analyze potential oligomerization of FAM134C in response to bacterial components like LPS

  • Identification of binding domains through mutational analysis of positively charged amino acid residues

• Cellular localization studies:

  • Immunofluorescence microscopy to track colocalization of FAM134C with bacterial components

  • Dual-color tagging systems (e.g., mCherry-EGFP-FAM134C) to monitor trafficking and localization in different cellular compartments

• Functional membrane assays:

  • Liposome-based membrane remodeling assays with purified recombinant FAM134C protein to assess its ability to induce membrane fragmentation

  • Empty liposomes could be added to FAM134C recombinant protein at different lipid-to-protein ratios (LPR) such as 100:1 or 40:1 to assess membrane interaction capabilities

What is the potential role of FAM134C in pathogen-host interactions?

Based on insights from FAM134B studies, FAM134C may play significant roles in pathogen-host interactions:

• Bacterial component sensing:
  FAM134C binds to bacterial LPS with similar efficiency to FAM134B , suggesting it may function as a cytosolic sensor for bacterial components.

• Membrane remodeling in response to infection:
  FAM134B induces ER fragmentation upon binding to LPS, with the lipid A component mediating binding and the O-antigen component triggering oligomerization and membrane fragmentation . FAM134C may have similar capabilities in membrane remodeling during infection.

• Vacuole formation and bacterial survival:
  FAM134B-positive structures are recruited to bacteria-containing vacuoles, potentially creating niches for bacterial survival . Studies show that FAM134B-positive Salmonella-containing vacuoles are not acidified, providing a niche for Salmonella survival . It would be valuable to investigate whether FAM134C performs similar functions.

• Regulation of immune responses:
  The interaction between FAM134C and bacterial components may influence immune signaling pathways, similar to other cytosolic pattern recognition receptors.

How do the different components of LPS interact with FAM134 family proteins?

The interaction between LPS and FAM134 family proteins involves distinct roles for different LPS components as demonstrated with FAM134B:

• Lipid A interactions:

  • Lipid A of LPS directly binds to FAM134B via electrostatic forces, interacting with positively charged amino acid residues on the amphipathic helices and C-terminal region of the protein

  • While lipid A is sufficient for binding, it does not induce oligomerization of FAM134B

• O-antigen (O-Ag) interactions:

  • O-Ag of LPS is indispensable for the oligomerization of FAM134B

  • Infection with O-Ag-defective bacterial strains (including rfbP, rfaL, rfaG, and rfaH mutants) significantly reduced FAM134B oligomers compared to wild-type strains

  • O-Ag triggers FAM134B oligomerization which drives subsequent membrane fragmentation

Based on the high sequence similarity between FAM134B and FAM134C , similar interaction patterns with LPS components might be expected for FAM134C, though specific experimental validation is necessary.

What are the optimal storage and handling conditions for recombinant Xenopus tropicalis FAM134C protein?

Based on the product information, the following storage and handling conditions are recommended for recombinant Xenopus tropicalis FAM134C protein:

• Storage conditions:

  • Store lyophilized powder at -20°C/-80°C upon receipt

  • After reconstitution, store aliquots at -20°C/-80°C for long-term storage

  • Working aliquots can be stored at 4°C for up to one week

• Reconstitution protocol:

  • Briefly centrifuge the vial before opening to bring contents to the bottom

  • Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

  • Add glycerol to a final concentration of 5-50% (recommended 50%) and aliquot for long-term storage

• Handling recommendations:

  • Avoid repeated freeze-thaw cycles as they can compromise protein integrity

  • Use sterile techniques when handling the protein

  • For optimal activity, use freshly reconstituted protein or minimize freeze-thaw cycles

What assays can be used to analyze FAM134C oligomerization and membrane remodeling activities?

Based on methodologies used with FAM134B, the following assays can be adapted to study FAM134C oligomerization and membrane remodeling:

• Oligomerization analysis:

  • Blue native PAGE followed by immunoblotting: This technique enforces migration of native protein complexes based solely on their molecular weight, allowing detection of oligomeric species

  • Chemical crosslinking assays to stabilize transient oligomeric interactions

  • Size exclusion chromatography to separate monomeric and oligomeric species

• Membrane remodeling assays:

  • In vitro liposome membrane remodeling assays: Incubating purified recombinant FAM134C with artificial liposomes at different lipid-to-protein ratios (e.g., 100:1 or 40:1)

  • Electron microscopy to visualize membrane deformation and fragmentation

  • Fluorescence microscopy with labeled liposomes to track membrane dynamics

• Cellular ER fragmentation analysis:

  • Expression of fluorescently tagged ER markers along with FAM134C to monitor ER morphology changes

  • Live-cell imaging to track real-time membrane dynamics

  • Dual-color systems (e.g., mCherry-EGFP-FAM134C) to monitor trafficking and acidification of FAM134C-positive structures

How can the binding affinity between FAM134C and bacterial components be quantified?

Several biophysical and biochemical techniques can be employed to quantify binding affinity between FAM134C and bacterial components:

• Surface Plasmon Resonance (SPR):

  • Immobilize purified recombinant FAM134C on a sensor chip

  • Flow different concentrations of purified LPS or lipid A over the chip

  • Measure association and dissociation kinetics to determine KD values

  • This technique allows real-time, label-free detection of molecular interactions

• Isothermal Titration Calorimetry (ITC):

  • Directly measure thermodynamic parameters of binding

  • Provides binding affinity (KD), stoichiometry, and thermodynamic parameters (ΔH, ΔS)

• Microscale Thermophoresis (MST):

  • Label FAM134C with a fluorescent dye

  • Measure changes in thermophoretic mobility upon binding to bacterial components

  • Requires small sample volumes and can work with a wide range of buffer conditions

• Biolayer Interferometry (BLI):

  • Similar principle to SPR but uses optical interference patterns

  • Good for analyzing kinetics of association and dissociation

• Biochemical pull-down quantification:

  • Adapt the biotin-LPS pulldown approach used for FAM134B

  • Use increasing concentrations of competitors to determine relative binding affinities

  • Quantify bound proteins through western blotting or mass spectrometry

What cell models are most appropriate for studying FAM134C function?

Based on research approaches with related proteins, several cell models would be appropriate for studying FAM134C function:

• Mammalian cell lines:

  • HeLa cells: Widely used for studying membrane dynamics and protein trafficking

  • HEK293T cells: Good for protein overexpression and purification

  • Bone marrow-derived macrophages (BMDMs): Appropriate for studying FAM134C in immune contexts, as used for FAM134B studies

• Xenopus-based models:

  • Xenopus tropicalis cell lines: Provide a species-matched cellular environment for studying the native function of Xenopus tropicalis FAM134C

  • Xenopus embryos/tadpoles: For studying developmental roles of FAM134C

• Knockout and knockdown models:

  • CRISPR/Cas9-generated FAM134C knockout cells

  • siRNA or shRNA-mediated FAM134C knockdown models

  • FAM134C inducible expression systems similar to the mCherry-EGFP-FAM134B inducible HeLa cells used in FAM134B studies

• Infection models:

  • Cells infected with bacterial pathogens like Salmonella to study FAM134C recruitment to bacteria-containing vacuoles

  • Cells treated with bacterial outer membrane vesicles (OMVs) to study LPS delivery and resulting FAM134C activation

How can mutations in FAM134C be designed to study its binding specificity to bacterial components?

Based on the FAM134B mutation studies, several strategic approaches can be applied to investigate FAM134C binding specificity:

• Targeted mutagenesis of charged residues:

  • Identify positively charged amino acid residues (lysine, arginine) in the amphipathic helices and C-terminal region of FAM134C that might interact with negatively charged lipid A

  • Generate single, double, and triple mutants with charged-to-neutral amino acid substitutions

  • Test binding capacity through co-immunoprecipitation or pulldown assays similar to those used for FAM134B

• Domain swapping experiments:

  • Generate chimeric proteins between FAM134C and FAM134A (which shows weaker LPS binding)

  • Map the critical regions responsible for bacterial component binding

• Deletion constructs:

  • Create truncation mutants to identify the minimal binding domain

• LC3-interaction region (LIR) mutations:

  • Generate LIR mutants to distinguish between binding to bacterial components and autophagy functions

  • Compare WT FAM134C with LIR mutant FAM134C in bacterial infection contexts

These approaches can help dissect the specific regions and amino acids in FAM134C responsible for bacterial component interactions.

What are the challenges in purifying and maintaining functional recombinant FAM134C protein?

Several challenges exist in the purification and maintenance of functional recombinant FAM134C:

• Membrane protein solubility:

  • FAM134C contains hydrophobic domains that can cause aggregation during expression and purification

  • Optimization of detergents or amphipols may be necessary to maintain proper folding

• Proper folding and post-translational modifications:

  • E. coli expression systems lack eukaryotic post-translational modification machinery

  • Consider eukaryotic expression systems for studies requiring native modifications

• Oligomerization state preservation:

  • Native oligomerization states may be disrupted during purification

  • Crosslinking approaches or native purification conditions may help preserve physiologically relevant oligomers

• Stability concerns:

  • Repeated freeze-thaw cycles should be avoided

  • The addition of stabilizing agents like trehalose (6%) in storage buffer helps maintain protein integrity

  • Glycerol (5-50%) addition is recommended for long-term storage

• Activity verification:

  • Functional assays should be established to verify that purified protein retains biological activity

  • Membrane binding and remodeling assays can serve as useful activity indicators

How might FAM134C function differently across species and developmental stages?

Understanding the evolutionary and developmental aspects of FAM134C function presents several research opportunities:

• Comparative analysis across species:

  • Compare Xenopus tropicalis FAM134C with mammalian orthologs to identify conserved and divergent functions

  • Investigate species-specific binding partners and regulatory mechanisms

  • Examine adaptation to different pathogen pressures across evolutionary lineages

• Developmental expression patterns:

  • Study temporal and spatial expression of FAM134C during embryonic development

  • Investigate potential roles in tissue modeling and organogenesis

• Tissue-specific functions:

  • Compare FAM134C function across different tissue types

  • Identify tissue-specific binding partners and regulatory mechanisms

• Specialization within the FAM134 family:

  • Investigate how functional specialization between FAM134A, FAM134B, and FAM134C evolved across species

  • Examine whether FAM134C plays more prominent roles in specific developmental contexts or tissue types

What future research directions could advance our understanding of FAM134C function?

Several promising research directions could enhance our understanding of FAM134C:

• Structural studies:

  • Determine the crystal or cryo-EM structure of FAM134C, particularly in complex with bacterial components

  • Investigate conformational changes upon binding to LPS or other bacterial factors

• Systems biology approaches:

  • Identify the complete interactome of FAM134C using mass spectrometry-based proteomics

  • Compare FAM134C interactome in normal versus infection conditions

• Role in disease contexts:

  • Investigate potential roles of FAM134C in infectious diseases, particularly those caused by Gram-negative bacteria

  • Explore connections to neurodegenerative diseases, as reticulophagy regulators have been implicated in such conditions

• Therapeutic targeting:

  • Explore whether modulation of FAM134C activity could influence bacterial survival during infection

  • Investigate small molecules that could modulate FAM134C-LPS interactions

• In vivo models:

  • Develop animal models with FAM134C mutations or tissue-specific deletion

  • Study consequences for ER homeostasis and response to bacterial infection