Recombinant Mouse Claudin-2 (Cldn2)

What is mouse Claudin-2 and what are its key structural characteristics?

Mouse Claudin-2 (Cldn2) is a tight junction protein belonging to the claudin family. It functions as a major integral membrane protein localized exclusively at tight junctions and plays a critical role in regulating paracellular permeability. The protein has a molecular weight of approximately 24.4 kDa and contains 230 amino acid residues . The recombinant form, depending on production system and tags, often appears at around 19.3-25 kDa in SDS-PAGE analysis . Structurally, Claudin-2 is expressed in an organ-specific manner, particularly in the intestine, and regulates tissue-specific physiological properties of tight junctions . The protein contains four transmembrane domains with both N- and C-termini located in the cytoplasm, forming paracellular channels that are cation-selective.

How does recombinant mouse Claudin-2 differ from native Claudin-2?

Recombinant mouse Claudin-2 maintains the core functional domains of native Claudin-2 but typically includes modifications to facilitate purification and detection in experimental settings. The recombinant protein often contains fusion tags such as His-tag, SUMO-tag, GST-tag, or Myc-DYKDDDDK (FLAG) tag . These modifications can affect the apparent molecular weight, with tagged recombinant Claudin-2 appearing larger on SDS-PAGE than predicted (e.g., 25 kDa observed vs. 19.3 kDa predicted) .

The expression systems also differ significantly from native conditions, with recombinant proteins typically produced in:

• Prokaryotic systems like E. coli (common for partial protein fragments)

• Eukaryotic systems such as HEK293 cells (for full-length protein with proper folding)

• Cell-free protein synthesis systems

• Wheat germ expression systems

Unlike native Claudin-2, recombinant versions may contain only specific regions of interest, such as amino acids 29-81 or 1-230, depending on the experimental requirements .

What expression systems are commonly used for mouse Claudin-2 production, and how do they compare?

Several expression systems are utilized for recombinant mouse Claudin-2 production, each with distinct advantages:

For mouse Claudin-2, prokaryotic expression in E. coli is commonly used for producing fragments (amino acids 29-81), yielding proteins with > 90% purity . For applications requiring full-length functional protein, mammalian expression systems like HEK293 cells are preferred, typically achieving > 80% purity as determined by SDS-PAGE .

What are the optimal storage and reconstitution conditions for recombinant mouse Claudin-2?

Proper handling of recombinant mouse Claudin-2 is crucial for maintaining its stability and functionality:

Storage conditions:

• Recommended storage temperature: -80°C for long-term stability

• Avoid repeated freeze-thaw cycles (limit to 2-3 cycles)

• When received as freeze-dried powder, store at -20°C until reconstitution

Reconstitution protocol:

• Reconstitute in appropriate buffer - typically 20mM Tris, 150mM NaCl (pH 8.0) to a concentration of 0.1-1.0 mg/mL

• Do not vortex the solution, as this can denature membrane proteins like Claudin-2

• For working aliquots, thaw samples on ice

• After initial thawing, immediately aliquot into single-use tubes before re-freezing

Alternative buffer formulations include 25 mM Tris-HCl, pH 7.3, with 100 mM glycine and 10% glycerol for specific applications . For optimal protein stability, addition of stabilizers like trehalose (5%) and surfactants (0.01% SKL) can enhance shelf-life .

How can I validate the purity and activity of recombinant mouse Claudin-2 for my experiments?

A multi-faceted approach ensures proper validation of recombinant mouse Claudin-2:

Purity assessment methods:

• SDS-PAGE with Coomassie blue staining (expect > 80-90% purity)

• Western blot using anti-Claudin-2 or anti-tag antibodies

• Analytical size exclusion chromatography (SEC-HPLC)

Functional validation approaches:

• Paracellular permeability assays using ion-selective electrodes or fluorescent tracers

• Electrophysiological measurements in transfected cells

• Tight junction reconstitution assays

When interpreting SDS-PAGE results, note that the observed molecular weight (≈25 kDa) may differ from the predicted value (≈19.3 kDa) due to factors including:

• Relative charge contributions from amino acid composition

• Post-translational modifications

• Influence of fusion tags

• Aberrant migration behavior common to membrane proteins

For applications requiring confirmation of selective cation permeability (a key functional characteristic of Claudin-2), assays measuring Na+, methylamine, and ethylamine flux across epithelial monolayers provide quantitative validation .

What experimental controls should be included when working with recombinant mouse Claudin-2?

Positive controls:

• Wild-type claudin-2 expressing cells or tissues (e.g., intestinal crypts)

• Previously validated recombinant Claudin-2 protein batch

• IL-13 treated samples (known to upregulate Claudin-2)

Negative controls:

• Claudin-2 knockout (Cldn2-/-) cells or tissues

• Isotype-matched irrelevant protein with similar tag system

• Buffer-only conditions

Specificity controls:

• Other claudin family members (e.g., Claudin-14, Claudin-23) to assess selectivity

• Competitive binding assays with unlabeled protein

• Tag-only protein constructs to distinguish tag artifacts from Claudin-2 effects

When conducting genetic knockout experiments, validation through ICE (Inference of CRISPR Edits) analysis is recommended, with efficiency values >90% indicating successful Cldn2 gene editing . For transgenic overexpression studies, confirming localization at tight junctions using immunofluorescence microscopy is essential .

How can recombinant mouse Claudin-2 be used to study intestinal barrier function?

Recombinant mouse Claudin-2 serves as a powerful tool for investigating intestinal barrier regulation through several sophisticated approaches:

Barrier reconstitution models:

• Addition of purified recombinant Claudin-2 to claudin-deficient epithelial cells

• Integration into artificial lipid bilayers to study channel formation

• Comparative studies between wild-type and mutant Claudin-2 variants

Molecular interaction studies:

• Protein-protein interaction assays to identify binding partners

• Overlay assays using labeled recombinant Claudin-2

• Pull-down experiments to isolate Claudin-2 complexes

Research has demonstrated that Claudin-2 creates paracellular channels selective for small cations (Na+) and water, with IL-13 treatment increasing Claudin-2 expression and concomitantly enhancing paracellular permeability to Na+, methylamine, and ethylamine in intestinal tissue . This selective permeability can be recapitulated by transgenic expression of GFP-Claudin-2, confirming Claudin-2's direct role in regulating barrier function .

Interestingly, Claudin-2 effects on barrier function appear context-dependent: in infectious and chemical colitis models, Claudin-2 knockout augments disease severity, while overexpression is protective. This contrasts with immune-mediated colitis, where transgenic Claudin-2 expression exacerbates disease . These findings suggest that Claudin-2-mediated pore pathway permeability may represent an adaptive response in some inflammatory contexts but be detrimental in others.

What is known about Claudin-2's role in cancer progression, and how can recombinant protein help study these mechanisms?

Claudin-2 has emerged as a significant regulator in cancer biology, particularly in colorectal cancer (CRC):

Key findings on Claudin-2 in cancer:

• High Claudin-2 expression correlates with decreased cancer-specific survival in CRC patients

• Claudin-2 promotes CRC development and metastasis by inhibiting NDRG1 transcription

• Claudin-2 affects cancer cell growth and migration/invasion via EGFR-mediated signaling transactivation

• High Claudin-2 expression is associated with worse prognosis and increased recurrence risk in stage II/III CRC patients receiving adjuvant treatment

Research applications of recombinant Claudin-2:

• Structure-function studies using domain-specific mutants

• Signaling pathway analysis in cancer cells

• Development of blocking agents targeting Claudin-2 interactions

CRISPR/Cas9-mediated knockout of Claudin-2 in HCT116 colon cancer cells revealed widespread downregulation of genes linked to motility, invasion, and metastasis, including ZONAB, NDRG1, Claudin-14, Claudin-23, Bcl2, P53, and BCL-6 . This suggests that Claudin-2 functions as a master regulator of multiple pathways involved in cancer progression. Recombinant Claudin-2 can be used to rescue expression in knockout cells, allowing precise determination of structure-function relationships and identification of critical domains responsible for these oncogenic effects.

How can recombinant mouse Claudin-2 be used for developing targeted therapeutics?

The involvement of Claudin-2 in intestinal barrier function and cancer progression makes it an attractive therapeutic target:

Target validation approaches:

• Epitope mapping using truncated recombinant Claudin-2 fragments

• Competition assays with extracellular loop-derived peptides

• High-throughput screening of compound libraries against recombinant Claudin-2

Therapeutic development strategies:

• Claudin-2 channel blockers for treating barrier dysfunction

• Claudin-2 expression modulators for cancer therapy

• Anti-Claudin-2 antibody development for targeted delivery

The dual and seemingly contradictory roles of Claudin-2 in different disease contexts require careful consideration when developing therapeutics. In infectious and chemical colitis, increasing Claudin-2 function may be beneficial, while in immune-mediated colitis and cancer, inhibition appears more promising .

For antibody development, recombinant mouse Claudin-2 with >80% purity is suitable for immunization protocols and for screening antibody specificity . The availability of various tagged versions (His-tag, SUMO-tag, GST-tag) facilitates different purification and detection strategies during therapeutic development .

How do mouse and human Claudin-2 compare, and what are the implications for translational research?

Understanding species differences is crucial for translating mouse-based findings to human applications:

Structural and functional comparisons:

Despite high conservation, species differences necessitate validation of mouse findings in human systems. Experimental approaches include:

• Comparative functional studies with recombinant proteins from both species

• Cross-species rescue experiments in knockout models

• Parallel analysis of transgenic mice expressing human Claudin-2

In colitis models, both mouse and human Claudin-2 transgenic expression appears protective in chemical (DSS) colitis but potentially harmful in immune-mediated colitis , suggesting conserved functional roles in inflammatory contexts.

What transgenic and knockout mouse models are available for studying Claudin-2 function?

Several genetic mouse models have been developed to investigate Claudin-2 function in vivo:

Knockout models:

• Cldn2-/- (complete knockout) - Shows delayed onset of immune-mediated colitis but increased risk of intestinal obstruction

• Tissue-specific conditional knockouts - Allow investigation of Claudin-2 function in specific cell types

Transgenic models:

• Cldn2 Tg (overexpression using Vil1 promoter) - Exhibits intestinal epithelium-specific expression of GFP-tagged Claudin-2

• Inducible transgenic models - Permit temporal control of Claudin-2 expression

Compound genetic models:

• Cldn2-/-Rag1-/- - Used to study immune-mediated colitis in the absence of Claudin-2

• Cldn2 TgRag1-/- - Allows investigation of Claudin-2 overexpression in immune-deficient backgrounds

These models have revealed complex, context-dependent roles for Claudin-2. In infectious and chemical colitis, Claudin-2 knockout exacerbated disease while overexpression was protective . Conversely, in immune-mediated colitis (T cell transfer model), transgenic Claudin-2 expression unexpectedly worsened disease outcomes . The recombinant protein can be used for rescue experiments in knockout models to confirm specificity of observed phenotypes.

How can cell-based assays be optimized using recombinant mouse Claudin-2?

Cell-based experimental systems provide controlled environments for investigating Claudin-2 function:

Cell line selection considerations:

• Endogenous Claudin-2 expression levels

• Presence of tight junction machinery

• Polarization capacity

• Transfection efficiency

Optimization strategies for recombinant Claudin-2 studies:

• Titration of recombinant protein concentration (typically 0.1-1.0 mg/mL)

• Adjustment of exposure time to determine acute vs. chronic effects

• Co-application with cytokines (e.g., IL-13) to modulate endogenous expression

• Combination with other tight junction proteins to study complex barrier regulation

Advanced cell-based applications:

• CRISPR/Cas9-mediated knockout followed by rescue with recombinant protein

• Structure-function analysis using domain-specific mutants

• Real-time imaging of barrier dynamics using labeled recombinant Claudin-2

The CRISPR/Cas9 system has been effectively used to create claudin-2 knockout in HCT116 colon cancer cells with high editing efficiency (91% INDL) . These edited cell lines, when compared to wild-type cells, revealed widespread downregulation of genes associated with cancer progression, including ZONAB, NDRG1, Claudin-14, and Claudin-23 .

Why might recombinant mouse Claudin-2 show different molecular weights in various experimental systems?

Discrepancies in observed molecular weight are common with membrane proteins like Claudin-2:

Common causes of molecular weight variations:

• Fusion tags influence: His-tag, SUMO-tag, GST-tag, or Myc-DYKDDDDK Tag can add significant mass to the protein

• Post-translational modifications: Especially in eukaryotic expression systems

• Protein-detergent complexes: Residual detergent binding can alter migration

• Relative charge effects: Amino acid composition affects SDS binding and mobility

• Conformational resistance: Incomplete denaturation of transmembrane domains

For recombinant mouse Claudin-2, the predicted molecular mass is often around 19.3 kDa, but the actual observed mass on SDS-PAGE under reducing conditions is approximately 25 kDa . This discrepancy is normal and expected due to the factors listed above.

When comparing different batches or sources of recombinant Claudin-2, standardization of electrophoresis conditions and marker systems is critical for consistent molecular weight determination. Western blotting with specific antibodies against either Claudin-2 or the fusion tag provides confirmation of protein identity despite migration anomalies.

What are the most common pitfalls when using recombinant mouse Claudin-2 in barrier function studies?

Several technical challenges can affect experiments investigating Claudin-2's role in barrier function:

Common pitfalls and solutions:

For accurate barrier function assessment, transgenic expression models that recapitulate physiological Claudin-2 distribution patterns often provide more reliable results than exogenous protein application . When using recombinant protein, careful titration studies should establish dose-response relationships.

How can I address reproducibility issues in Claudin-2 protein expression and purification?

Ensuring consistent production of functional recombinant mouse Claudin-2 requires attention to several critical factors:

Key reproducibility considerations:

• Expression system standardization

  • Maintain consistent cell passage numbers for mammalian expression

  • Use the same E. coli strain and growth conditions for prokaryotic expression

  • Document and control induction parameters (temperature, time, inducer concentration)

• Purification protocol optimization

  • Standardize buffer compositions (20mM Tris, 150mM NaCl, pH8.0)

  • Validate tag-based purification efficiency batch-to-batch

  • Implement quality control checkpoints throughout the purification process

• Storage and stability protocols

  • Aliquot purified protein to avoid freeze-thaw cycles

  • Store at recommended temperature (-80°C long-term)

  • Include stabilizers (5% trehalose, 0.01% SKL) for lyophilized preparations

• Validation metrics

  • Establish acceptance criteria for purity (typically >80-90% by SDS-PAGE)

  • Develop functional assays specific to Claudin-2 activity

  • Document protein concentration determination methods

Prokaryotic expression of partial Claudin-2 fragments (e.g., amino acids 29-81) typically yields higher quantities of protein but may lack proper folding for some applications . For studies requiring full functional activity, mammalian expression systems producing full-length Claudin-2 (amino acids 1-230) are preferred despite potentially lower yields .

How is recombinant Claudin-2 being used to explore its role in inflammatory bowel disease pathogenesis?

Recent research has uncovered complex roles for Claudin-2 in intestinal inflammation:

Key findings in inflammatory bowel disease models:

• Claudin-2 has context-dependent effects in different colitis models

• Protective in infectious (Citrobacter rodentium) and chemical (DSS) colitis

• Detrimental in immune-mediated (T cell transfer) colitis models

• Claudin-2 knockout leads to delayed disease onset in immune-mediated colitis

• Transgenic Claudin-2 expression exacerbates immune-mediated colitis

Current research applications:

• Investigating disease-specific Claudin-2 regulation in different IBD subtypes

• Exploring Claudin-2's role in epithelial repair and regeneration

• Examining interactions between Claudin-2 and immune cell populations

Studies using Cldn2-/-Rag1-/- and Cldn2 TgRag1-/- mice have revealed that Claudin-2 differentially affects inflammatory outcomes in immune-mediated colitis. Disease was significantly more severe in Cldn2 TgRag1-/- mice compared to Cldn2+/+Rag1-/- controls, with greater weight loss, higher disease activity scores, and increased permeability to both small and large molecules . Conversely, Cldn2-/- mice showed delayed disease onset and reduced inflammatory cytokine production . These findings suggest that while Claudin-2 upregulation may be adaptive in some inflammatory contexts, it appears detrimental in T cell-mediated inflammation.

What new techniques are being developed to study Claudin-2 protein-protein interactions?

Advances in molecular techniques are expanding our understanding of Claudin-2's interaction network:

Emerging methodologies:

• Proximity labeling techniques (BioID, APEX) to identify claudin-2 interactors in living cells

• Single-molecule tracking of fluorescently labeled recombinant Claudin-2

• Cryo-electron microscopy for structural analysis of Claudin-2 complexes

• High-throughput interactome mapping using protein arrays with recombinant Claudin-2

Recent findings:

• Claudin-2 interactions with ZONAB affect gene expression in cancer progression

• Claudin-2 inhibits NDRG1 transcription, promoting CRC development and metastasis

• Claudin-2 may interact with or regulate other claudin family members (Claudin-14, Claudin-23)

CRISPR/Cas9-mediated knockout of Claudin-2 in HCT116 cells revealed its regulatory influence on multiple genes associated with cancer progression, including ZONAB, NDRG1, Claudin-14, Claudin-23, Bcl2, P53, and BCL-6 . These findings suggest Claudin-2 functions not only as a structural tight junction protein but also as a signaling hub affecting transcriptional networks. Recombinant Claudin-2 protein is being used to validate direct interaction partners and to identify the specific domains responsible for these regulatory effects.

How might recombinant Claudin-2 contribute to development of targeted therapies for colorectal cancer?

The involvement of Claudin-2 in colorectal cancer progression presents therapeutic opportunities:

Therapeutic development approaches:

• Target validation strategies

  • Using recombinant Claudin-2 to screen for small molecule inhibitors

  • Developing neutralizing antibodies against specific Claudin-2 domains

  • Testing peptide mimetics that disrupt Claudin-2 protein-protein interactions

• Precision medicine applications

  • Correlating Claudin-2 expression levels with treatment responses

  • Identifying patient subgroups that might benefit from Claudin-2-targeted therapies

  • Developing companion diagnostics using anti-Claudin-2 antibodies

• Combination therapy exploration

  • Testing Claudin-2 inhibitors with established chemotherapeutics

  • Investigating synergistic effects with immune checkpoint inhibitors

  • Exploring interactions with radiation therapy

High Claudin-2 expression correlates with decreased cancer-specific survival rates and worse prognosis in stage II/III CRC patients receiving adjuvant treatment . CRISPR-mediated Claudin-2 knockout in colon cancer cells leads to downregulation of multiple genes associated with motility, invasion, and metastasis , suggesting that targeting Claudin-2 could simultaneously affect multiple cancer-promoting pathways. These findings position Claudin-2 as a promising therapeutic target for CRC, with recombinant protein serving as a valuable tool for drug discovery and development.