Phospho-CLDN5 (Y217) Antibody

Basic Research Questions

• What is Claudin-5 and what is the significance of its phosphorylation at tyrosine 217?

Claudin-5 (CLDN5) is a 23.1 kDa transmembrane protein consisting of 218 amino acids that plays a major role in tight junction-specific obliteration of intercellular spaces. It is primarily expressed in endothelial cells and is crucial for maintaining the integrity of barriers like the blood-brain barrier.

Phosphorylation at tyrosine 217 (Y217) is a post-translational modification that occurs in the C-terminal domain (amino acid region 169-218) of the protein. This specific phosphorylation has been implicated in the regulation of tight junction permeability and barrier function.

Methodologically, researchers study this phosphorylation using phospho-specific antibodies that detect CLDN5 only when phosphorylated at Y217, allowing for the investigation of signaling pathways that regulate barrier function in various physiological and pathological conditions .

• What are the recommended applications for Phospho-CLDN5 (Y217) antibodies in experimental research?

Based on validation data from multiple sources, Phospho-CLDN5 (Y217) antibodies can be reliably used in the following applications:

When designing experiments, it's important to note that optimal dilutions may vary depending on the specific antibody and experimental conditions. Validation in your particular experimental system is always recommended .

• What species reactivity is reported for commercially available Phospho-CLDN5 (Y217) antibodies?

Most Phospho-CLDN5 (Y217) antibodies demonstrate cross-reactivity across multiple species due to the high conservation of the phosphorylation site and surrounding sequence. The documented reactivity includes:

When working with species not explicitly validated, preliminary testing is necessary as the antibody's performance may vary despite sequence homology predictions .

• How should researchers optimize Western blot protocols for detecting phosphorylated CLDN5 at Y217?

For optimal Western blot results when detecting phosphorylated CLDN5 at Y217:

• Sample preparation:

  • Use phosphatase inhibitors in lysis buffers to preserve phosphorylation status

  • Consider using pervanadate treatment (50mM for 5 minutes) as a positive control to increase tyrosine phosphorylation

• Gel electrophoresis and transfer:

  • Use 10-15% gels for optimal resolution of the 23 kDa protein

  • Note that the observed band size may be approximately 20 kDa

• Blocking and antibody conditions:

  • Block with 5% non-fat dry milk in TBST

  • Use recommended antibody dilutions (typically 1:1000-1:50000 depending on the antibody)

  • Include phosphatase treatment controls to confirm specificity

• Controls and validation:

  • Include untreated and phosphatase-treated samples as negative controls

  • Use GAPDH or similar loading controls

  • For definitive validation, include alkaline phosphatase treatment of duplicate samples to demonstrate phospho-specificity

As demonstrated in validated Western blots, phosphorylation at Y217 is typically induced or enhanced in experimental conditions, allowing for clear demonstration of antibody specificity .

• What storage and handling conditions are recommended for maintaining Phospho-CLDN5 (Y217) antibody activity?

To maintain optimal antibody performance:

When working with the antibody:

• Briefly centrifuge the antibody vial before opening to collect liquid at the bottom

• Aliquot antibodies for frequent use to avoid repeated freeze-thaw cycles

• Return unused antibody to appropriate storage temperature promptly

• Monitor for signs of bacterial contamination or precipitation

Advanced Research Questions

• How can researchers validate the specificity of Phospho-CLDN5 (Y217) antibodies in their experimental systems?

A comprehensive validation approach should include:

• Phosphatase treatment controls:

  • Split samples and treat one portion with alkaline phosphatase for 1 hour

  • Compare antibody reactivity between treated and untreated samples

  • Complete loss of signal in phosphatase-treated samples confirms phospho-specificity

• Phosphorylation induction:

  • Use pervanadate (50mM) treatment to enhance tyrosine phosphorylation

  • Compare signal intensity between untreated and pervanadate-treated samples

  • Significant increase in signal after treatment supports phospho-specificity

• Immunoprecipitation validation:

  • Perform IP with the phospho-specific antibody

  • Compare IP from control versus phosphorylation-induced samples

  • Enrichment of the target protein only in the induced sample supports specificity

• Cross-validation with different antibody clones:

  • Compare results between monoclonal (e.g., EPR10810) and polyclonal antibodies

  • Concordant results with different antibodies increase confidence in specificity

These validation steps are particularly important for phospho-specific antibodies, as they can sometimes recognize other proteins or non-phosphorylated epitopes .

• What are the key differences between monoclonal and polyclonal Phospho-CLDN5 (Y217) antibodies for research applications?

The choice between monoclonal and polyclonal Phospho-CLDN5 (Y217) antibodies involves several considerations:

For critical research requiring absolute reproducibility, monoclonal antibodies may be preferred. For applications like IHC where epitope access might be variable, polyclonal antibodies often provide better results. Some researchers use both types in parallel for validation .

• How does the phosphorylation of Claudin-5 at Y217 affect blood-brain barrier function in disease models?

Phosphorylation of Claudin-5 at Y217 has significant implications for blood-brain barrier (BBB) integrity and function:

• Alzheimer's disease models:

  • Decreased Claudin-5 expression correlates with increased BBB permeability near Aβ plaques

  • Changes in phosphorylation state at Y217 are associated with fibrinogen leakage

  • Disruption of CLDN5 phosphorylation state contributes to decreased glucose transporter (Glut1) expression

• Experimental approaches to study BBB dysfunction:

  • Immunohistochemical co-staining of phospho-Y217 CLDN5 with vascular markers

  • Measurement of barrier permeability using tracer molecules

  • Correlation of phosphorylation events with tight junction organization

• Mechanistic considerations:

  • Y217 is located in the C-terminal domain (aa 169-218) that interacts with cytoplasmic scaffolding proteins

  • Phosphorylation likely alters these interactions, affecting tight junction assembly or stability

  • Kinase activation during inflammatory or disease states may regulate this phosphorylation event

Understanding these phosphorylation events provides potential therapeutic targets for disorders involving BBB dysfunction, including neurodegenerative diseases and stroke .

• What experimental approaches can be used to study the kinases responsible for CLDN5 Y217 phosphorylation?

To identify and characterize kinases that phosphorylate CLDN5 at Y217:

• Kinase inhibitor screening:

  • Treat cells expressing CLDN5 with panels of tyrosine kinase inhibitors

  • Monitor Y217 phosphorylation status using the phospho-specific antibody

  • Identify candidate kinases based on inhibition patterns

• In vitro kinase assays:

  • Express recombinant CLDN5 C-terminal domain (aa 169-218)

  • Perform in vitro kinase reactions with purified candidate kinases

  • Detect phosphorylation using phospho-Y217 antibodies or mass spectrometry

• Genetic approaches:

  • Employ siRNA/shRNA knockdown or CRISPR/Cas9 knockout of candidate kinases

  • Assess effects on basal and stimulated Y217 phosphorylation

  • Validate with rescue experiments using wild-type versus kinase-dead constructs

• Co-immunoprecipitation studies:

  • Use antibodies against CLDN5 to immunoprecipitate protein complexes

  • Analyze for the presence of candidate kinases

  • Perform reverse IP with kinase antibodies to confirm interaction

This multi-faceted approach can help establish the regulatory mechanisms controlling CLDN5 phosphorylation under both physiological and pathological conditions .

• What strategies can researchers employ to study the temporal dynamics of Claudin-5 Y217 phosphorylation in cellular systems?

To investigate the temporal dynamics of CLDN5 Y217 phosphorylation:

• Time-course experiments:

  • Treat cells with stimuli known to affect tight junction function (e.g., inflammatory cytokines, growth factors)

  • Collect samples at multiple timepoints (5min, 15min, 30min, 1h, 3h, 6h, 24h)

  • Analyze Y217 phosphorylation status by Western blot using phospho-specific antibodies

• Live-cell imaging approaches:

  • Generate FRET-based biosensors incorporating the CLDN5 phosphorylation domain

  • Express in appropriate cell types (e.g., endothelial cells)

  • Monitor phosphorylation events in real-time following stimulation

• Phosphatase inhibition studies:

  • Use pervanadate treatment (50mM) to inhibit tyrosine phosphatases

  • Monitor the accumulation rate of phospho-Y217 CLDN5

  • Calculate phosphorylation/dephosphorylation kinetics

• Correlation with barrier function:

  • Simultaneously measure transendothelial/epithelial electrical resistance (TEER)

  • Assess paracellular permeability using fluorescent tracers

  • Correlate temporal changes in Y217 phosphorylation with functional barrier alterations