Recombinant Chicken Adenosine receptor A2b (ADORA2B)

What is Adenosine Receptor A2b (ADORA2B)?

Adenosine Receptor A2b (ADORA2B) is a protein belonging to the adenosine receptor group of G-protein-coupled receptors, which includes A1, A2A, and A3 receptors . In humans, ADORA2B is encoded by the ADORA2B gene located near the Smith-Magenis syndrome region on chromosome 17 . This integral membrane protein contains seven transmembrane domains and is 332 amino acids long in humans . The chicken ADORA2B protein (O13076) is slightly longer at 340 amino acids .

ADORA2B functions by stimulating adenylate cyclase activity when adenosine is present and interacts with netrin-1, which is involved in axon elongation . The receptor plays crucial roles in cellular signaling pathways, including those related to inflammation, hypoxia response, and immune regulation .

What are the primary biological functions of ADORA2B?

ADORA2B serves several critical biological functions, particularly in inflammatory and hypoxic conditions. The receptor is activated under high extracellular adenosine concentrations, such as those found in inflammatory environments or hypoxic conditions, including tumor microenvironments .

One of the most significant functions of ADORA2B is its potent anti-inflammatory role . Research has demonstrated that ADORA2B activation enhances the abundance of regulatory T cells (Tregs), which are critical in constraining inflammation . Studies using ADORA2B-deficient mice showed that these animals experienced more severe inflammation, characterized by increased cell recruitment and fluid leakage into airways during endotoxin-induced pulmonary inflammation .

ADORA2B also participates in various cellular processes including:

• Immunomodulation that may protect tumor cells

• Angiogenesis and metastasis in cancer contexts

• Interaction with netrin-1 for axon elongation and cAMP production

• Signal transduction via adenylate cyclase activation

The receptor shows high expression levels in specific tissues such as the bladder, colon, and cecum, with lower levels in blood vessels, lung, and eye tissues .

What are the recommended storage and reconstitution protocols for recombinant chicken ADORA2B?

For optimal storage and handling of recombinant chicken ADORA2B protein, researchers should follow these methodological guidelines:

Storage recommendations:

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

• Aliquot the reconstituted protein to avoid repeated freeze-thaw cycles, which can degrade the protein

• For working aliquots, store at 4°C for up to one week

• For long-term storage, add glycerol to a final concentration of 5-50% (50% is recommended) and store at -20°C/-80°C

Reconstitution protocol:

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

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

• Ensure complete dissolution by gentle mixing

• Add glycerol to the desired final concentration if storing long-term

• Aliquot to minimize freeze-thaw cycles

The reconstituted protein is typically stored in Tris/PBS-based buffer with 6% Trehalose at pH 8.0 . Following these protocols will help maintain protein integrity and biological activity for experimental applications.

How can researchers validate the functionality of recombinant chicken ADORA2B protein?

Validating the functionality of recombinant chicken ADORA2B requires multiple complementary approaches to ensure the protein maintains its native properties:

• Ligand binding assays:

  • Radioligand binding using specific adenosine receptor agonists/antagonists

  • Competition binding assays to determine binding affinity (Kd) and specificity

  • Saturation binding experiments to quantify receptor density

• Signal transduction validation:

  • cAMP accumulation assays (since ADORA2B stimulates adenylate cyclase activity)

  • Calcium mobilization measurements

  • Measuring phosphorylation of downstream effectors like MAPK and ERK

• Functional cellular assays:

  • T cell regulatory assays to assess ADORA2B's ability to enhance Treg abundance

  • Anti-inflammatory effect assessment in cell culture models

  • Netrin-1 interaction studies to confirm axon elongation functions

• Protein integrity verification:

  • SDS-PAGE to confirm protein purity (should be >90%)

  • Western blot using anti-His tag antibodies to verify expression

  • Circular dichroism to assess proper protein folding

• Comparative analysis:

  • Side-by-side comparison with human ADORA2B responses

  • Dose-response curves compared to published reference data

These validation approaches ensure that the recombinant protein maintains structural integrity and functional properties comparable to the native receptor.

What expression systems are optimal for producing functional recombinant chicken ADORA2B?

Several expression systems can be used to produce recombinant chicken ADORA2B, each with advantages and limitations for specific research applications:

E. coli expression system:

• Currently used for commercial recombinant chicken ADORA2B production

• Advantages: High yield, cost-effective, rapid production

• Limitations: May lack post-translational modifications, potential folding issues with transmembrane proteins

• Optimization: Using specialized E. coli strains (e.g., Rosetta, Origami) and fusion tags (His-tag) improves expression

Mammalian cell expression systems:

• Advantages: Proper protein folding, post-translational modifications, membrane integration

• Cell lines: HEK293, CHO cells provide environment similar to native conditions

• Applications: Ideal for functional studies and when membrane insertion is critical

Insect cell/baculovirus system:

• Advantages: Higher yield than mammalian cells, maintains most post-translational modifications

• Applications: Good compromise between bacterial and mammalian systems for GPCR expression

Cell-free expression systems:

• Advantages: Rapid production, ability to incorporate modified amino acids

• Applications: Useful for structural studies and when cytotoxicity is a concern

Yeast expression systems:

• Relevant for ADORA2B given previous work with random mutagenesis of human ADORA2B in yeast

• Advantages: Eukaryotic processing, cost-effective scaling

• Applications: Mutational studies, protein engineering

How can ADORA2B be utilized in studying inflammatory disease models?

ADORA2B plays a crucial role in modulating inflammatory responses, making it a valuable target for inflammatory disease research. Methodological approaches for utilizing ADORA2B in inflammatory disease models include:

Pulmonary inflammation models:

• Endotoxin-induced lung inflammation provides an excellent model to study ADORA2B function

• Previous research showed ADORA2B-deficient mice experienced more severe inflammation with increased cellular recruitment and fluid leakage into airways

• Methodology: Compare wild-type and ADORA2B-knockout models, measuring inflammatory markers, cellular infiltration, and regulatory T cell responses

Regulatory T cell modulation studies:

• ADORA2B activation enhances Treg abundance during inflammation

• Experimental approach: Use recombinant ADORA2B in vitro to examine direct effects on T cell differentiation

• Measure Treg induction, proliferation, and suppressive capacity under various inflammatory conditions

Pharmacological intervention testing:

• Screen compounds for selective ADORA2B modulation

• Methodology: Use recombinant chicken ADORA2B alongside human ADORA2B for comparative pharmacology

• Parameters to measure include receptor binding affinity, activation of downstream signaling, and functional outcomes in cellular models

Hypoxia-inflammation interaction studies:

• ADORA2B is activated under high extracellular adenosine concentrations during hypoxia

• Experimental design: Create controlled hypoxic conditions and measure ADORA2B activation and downstream effects

• Applications include ischemia-reperfusion injury models and tumor microenvironment studies

When designing these experiments, researchers should consider:

• Species-specific differences between chicken and mammalian ADORA2B

• Potential confounding effects from other adenosine receptors (A1, A2A, A3)

• Temporal dynamics of ADORA2B expression and activation during inflammatory processes

• Appropriate controls including selective receptor antagonists

What techniques can be used to study ADORA2B interaction with netrin-1 in axon elongation?

The interaction between ADORA2B and netrin-1 in axon elongation represents an important neurobiological function of this receptor . Researchers can employ several methodologies to investigate this interaction:

Co-immunoprecipitation (Co-IP) assays:

• Use anti-His tag antibodies to pull down recombinant chicken ADORA2B

• Detect bound netrin-1 using specific antibodies

• Control experiments should include other adenosine receptor subtypes to confirm specificity

Proximity ligation assays (PLA):

• Visualize ADORA2B-netrin-1 interactions in situ with subcellular resolution

• Applicable in neuronal cell cultures or tissue sections

• Quantify interaction events in different cellular compartments

FRET/BRET assays:

• Tag ADORA2B and netrin-1 with appropriate fluorophores/bioluminescent proteins

• Measure energy transfer as indicator of molecular proximity

• Allows real-time monitoring of interactions in living cells

Functional axon growth assays:

• Primary neuronal cultures from chicken embryos

• Measure axon elongation parameters (length, branching, directionality)

• Compare responses in the presence of:

  • ADORA2B agonists/antagonists

  • Netrin-1 with or without ADORA2B blockade

  • Mutated forms of ADORA2B that affect netrin-1 binding

cAMP production measurements:

• Since netrin-1-mediated axon outgrowth requires cAMP production through ADORA2B

• Use ELISA or FRET-based sensors to measure cAMP levels

• Compare wild-type conditions to those with ADORA2B knockdown/blockade

Advanced microscopy techniques:

• Live-cell imaging of fluorescently tagged proteins

• Super-resolution microscopy to visualize interaction sites

• Manipulate ADORA2B activity during imaging to capture dynamic changes

These methodologies can be combined to provide comprehensive insights into the molecular mechanisms underlying ADORA2B-netrin-1 interactions and their functional consequences in neuronal development and axon guidance.

How does ADORA2B signaling differ between avian and mammalian systems?

Understanding the evolutionary differences in ADORA2B signaling between avian (chicken) and mammalian systems provides valuable insights into adenosine receptor biology. Several methodological approaches can help elucidate these differences:

Comparative sequence and structure analysis:

• The chicken ADORA2B is 340 amino acids compared to 332 amino acids in humans

• Sequence alignment reveals conserved functional domains versus species-specific regions

• Homology modeling can predict structural differences in binding pockets and interaction interfaces

Signaling pathway comparison:

• Adenylate cyclase activation: Measure cAMP production in response to identical stimuli

• MAPK pathway activation: Compare phosphorylation patterns of p38 and ERK

• G-protein coupling preference: Determine if chicken ADORA2B couples to the same G-protein subtypes as mammalian counterparts

Pharmacological profiling:

• Conduct comparative pharmacology using the same panel of agonists/antagonists

• Parameters to compare:

  • Binding affinity (Kd values)

  • Potency (EC50/IC50 values)

  • Efficacy (maximum response)

  • Residence time (association/dissociation kinetics)

Cell type-specific expression patterns:

• In mammals, ADORA2B displays high expression in bladder, colon, and cecum

• Comparative immunohistochemistry and transcriptomics can identify species-specific expression patterns

• Functional significance of expression differences can be examined through tissue-specific assays

Interaction with regulatory proteins:

• E3KARP and Ezrin association with ADORA2B upon agonist stimulation has been studied in mammalian systems

• Investigate whether the same interactions occur with chicken ADORA2B

• Identify avian-specific interaction partners through proteomics approaches

Immunological function differences:

• Mammalian ADORA2B enhances regulatory T cell abundance

• Compare T cell responses in avian vs. mammalian systems using recombinant proteins

• Assess conservation of anti-inflammatory mechanisms across species

Understanding these differences is particularly valuable for researchers using chicken models to study ADORA2B function, as it helps determine which findings might translate to mammalian systems and identifies unique aspects of avian adenosine signaling.

What are common challenges in expressing and purifying functional recombinant ADORA2B?

Researchers working with recombinant ADORA2B often encounter several technical challenges during expression and purification. Here are methodological solutions to address these issues:

Membrane protein solubility issues:

• ADORA2B is a seven-transmembrane domain protein, making it inherently difficult to solubilize

• Solution: Use specialized detergents (DDM, LMNG, or CHS) during extraction

• Alternative approach: Consider fusion with solubility-enhancing tags (MBP, SUMO) beyond the standard His-tag

Protein misfolding in E. coli:

• E. coli expression often results in inclusion bodies of misfolded protein

• Solution: Optimize growth conditions (lower temperature, reduced induction)

• Alternative: Use specialized E. coli strains with enhanced disulfide bond formation capabilities

• For severe cases: Consider switching to eukaryotic expression systems

Low expression yields:

• GPCRs typically express at lower levels than soluble proteins

• Solution: Codon optimization for the expression host

• Protocol modification: Extend induction time with lower inducer concentration

• Advanced approach: High-density fermentation with controlled feeding

Protein degradation during purification:

• ADORA2B may be susceptible to proteolytic degradation

• Solution: Include protease inhibitor cocktail in all buffers

• Process modification: Perform purification at 4°C and minimize processing time

• Quality control: Monitor purity via SDS-PAGE at each purification step

Loss of functionality:

• Purified protein may lose native conformation and activity

• Solution: Validate functionality through binding assays after purification

• Alternative approach: Consider native-like membrane environments (nanodiscs, liposomes)

• For critical applications: Perform activity assays in parallel with purification steps

Aggregation during storage:

• Membrane proteins are prone to aggregation

• Solution: Store in buffer containing glycerol (5-50%)

• Best practice: Aliquot to avoid freeze-thaw cycles

• For lyophilized protein: Include stabilizers like trehalose (6%) in the buffer

Implementing these methodological solutions can significantly improve the quality and yield of functional recombinant ADORA2B protein for research applications.

How can researchers differentiate between ADORA2B-specific effects and those mediated by other adenosine receptors?

Distinguishing ADORA2B-specific effects from those mediated by other adenosine receptors (A1, A2A, and A3) is crucial for accurate interpretation of experimental results. Here are methodological approaches to achieve this differentiation:

Pharmacological approaches:

• Use receptor subtype-selective agonists and antagonists

• Employ concentration gradients to exploit differences in binding affinities between receptor subtypes

• Control experiments should include selective blockade of non-A2B receptors

• Validate findings using multiple, structurally distinct selective compounds

Genetic manipulation strategies:

• ADORA2B gene knockout or knockdown (siRNA, shRNA, CRISPR-Cas9)

• Rescue experiments with selective re-expression of ADORA2B

• Use of ADORA2B-deficient mouse models for in vivo studies

• Heterologous expression systems with single receptor subtypes

Expression analysis:

• Quantify relative expression levels of all adenosine receptor subtypes in the study system

• Correlate receptor expression with functional outcomes

• Use receptor subtype-specific antibodies for protein localization studies

• Consider single-cell analysis to account for cellular heterogeneity

Signaling pathway discrimination:

• A2B primarily couples to Gs proteins (increasing cAMP), while A1 and A3 couple to Gi (decreasing cAMP)

• Measure specific second messengers associated with different receptor subtypes

• Use pathway inhibitors to block specific downstream effectors

• Monitor temporal dynamics of signaling to identify receptor-specific patterns

Controlled experimental design:

• Include positive controls with known receptor-selective responses

• Perform parallel experiments in systems with defined receptor expression profiles

• Use concentration-response curves rather than single-dose experiments

• Account for potential receptor heteromerization in native systems

By combining these approaches, researchers can build a strong case for ADORA2B-specific effects and minimize confounding influences from other adenosine receptor subtypes, leading to more reliable and reproducible research findings.

What are the key considerations for translating findings from chicken ADORA2B to human applications?

Translating research findings from chicken ADORA2B studies to human applications requires careful consideration of species differences and methodological approaches that enhance translational validity:

Sequence and structural comparisons:

• Conduct detailed alignment of chicken (340 aa) and human (332 aa) ADORA2B sequences

• Focus particularly on:

  • Ligand binding domains

  • G-protein coupling interfaces

  • Regulatory phosphorylation sites

  • Membrane-spanning regions

• Use homology modeling to predict structural conservation and divergence

Functional conservation assessment:

• Compare signaling pathways activated by both receptors:

  • cAMP production via adenylate cyclase stimulation

  • MAPK and ERK activation patterns

  • Interaction with netrin-1 and downstream effects

• Validate key findings in both species using identical experimental conditions

Pharmacological profiles:

• Establish comparative pharmacology using the same compound libraries

• Parameters to compare include:

  • Binding affinities

  • Potency in functional assays

  • Off-target effects

  • Metabolic stability across species

• Identify compounds with consistent effects across species as potential translational candidates

Physiological relevance:

• Consider differences in expression patterns between species

• Evaluate whether the anti-inflammatory role of ADORA2B in enhancing regulatory T cells is conserved

• Account for potential differences in immune system regulation between avian and mammalian models

Validation in human systems:

• Confirm key findings in:

  • Human cell lines

  • Primary human cells

  • Human tissue samples where ethically available

  • Humanized mouse models

• Compare with existing human ADORA2B literature

Evolutionary context consideration:

• Assess conservation of ADORA2B function within the phylogenetic context

• Determine whether the pathway of interest emerged before or after avian-mammalian divergence

• Consider adaptive pressures that might have altered receptor function between species

By systematically addressing these considerations, researchers can better evaluate which findings from chicken ADORA2B studies are likely to translate to human biology and which may represent species-specific phenomena, ultimately enhancing the translational impact of their research.

How is ADORA2B being investigated in cancer research?

ADORA2B has emerged as a significant target in cancer research due to its activation in tumor microenvironments where high extracellular adenosine concentrations prevail under hypoxic conditions . Several methodological approaches are being employed to investigate ADORA2B in oncology:

Tumor microenvironment modulation:

• ADORA2B activation occurs under hypoxic conditions common in tumors

• Research methodologies include:

  • Co-culture systems modeling tumor-immune cell interactions

  • 3D spheroid models with oxygen gradients

  • In vivo tumor models with real-time oxygen monitoring

• Investigate how ADORA2B signaling affects stromal cells, immune infiltrates, and cancer cells

Immunomodulatory effects in cancer:

• ADORA2B enhances regulatory T cells, which may promote tumor immune evasion

• Experimental approaches:

  • Flow cytometry analysis of tumor-infiltrating lymphocytes

  • Ex vivo functional assessment of Tregs from tumor tissue

  • Combination studies with immune checkpoint inhibitors

• Examination of ADORA2B blockade as a strategy to enhance anti-tumor immunity

Angiogenesis and metastasis:

• ADORA2B participates in angiogenesis and metastasis processes

• Research methods include:

  • In vitro tube formation assays with endothelial cells

  • Invasion and migration assays with cancer cell lines

  • In vivo metastasis models with receptor-specific manipulations

• Evaluate receptor antagonists as potential anti-metastatic therapies

Therapeutic targeting strategies:

• Develop selective ADORA2B antagonists for cancer therapy

• Evaluate combination approaches with standard-of-care treatments

• Assess targeted delivery systems to enhance tumor specificity

• Identify biomarkers predicting response to ADORA2B-targeted therapy

Comparative models using recombinant proteins:

• Use recombinant chicken ADORA2B alongside human ADORA2B

• Compare pharmacological responses to identify broadly effective vs. species-specific compounds

• Develop structure-activity relationships for optimized drug design

This research direction offers promising opportunities for novel therapeutic approaches in cancer, particularly in addressing tumor-promoting inflammation and immune evasion mechanisms.

What role does ADORA2B play in neurological research beyond axon elongation?

While ADORA2B's interaction with netrin-1 in axon elongation is well-documented , emerging research is uncovering broader roles for this receptor in neurological function and pathology:

Neuroinflammatory regulation:

• ADORA2B's anti-inflammatory properties have implications for neuroinflammatory conditions

• Research approaches include:

  • Microglial activation studies in presence of ADORA2B modulators

  • Astrocyte inflammatory response assessment

  • Blood-brain barrier integrity models

• Applications in multiple sclerosis, Alzheimer's disease, and traumatic brain injury research

Synaptic plasticity modulation:

• Adenosine signaling affects synaptic strength and plasticity

• Methodological approaches:

  • Electrophysiological recordings (patch-clamp, field potentials)

  • Calcium imaging in neuronal cultures

  • Long-term potentiation/depression paradigms with ADORA2B-selective compounds

• Investigate ADORA2B's role in learning and memory processes

Neuron-glia interactions:

• ADORA2B signaling in astroglioma cells is altered by stimulation of bradykinin or interleukin receptors

• Research strategies:

  • Co-culture systems of neurons with glia

  • Selective manipulation of receptor expression in specific cell types

  • In vivo models with cell type-specific receptor deletion

• Examine bidirectional communication mediated by ADORA2B

Neurodevelopmental processes:

• Beyond axon elongation, investigate ADORA2B in:

  • Neural progenitor proliferation and differentiation

  • Migration patterns during development

  • Circuit formation and refinement

• Use embryonic chicken models leveraging recombinant ADORA2B

Neuroprotection in hypoxic/ischemic conditions:

• ADORA2B activation during hypoxia may be neuroprotective

• Experimental models:

  • Oxygen-glucose deprivation in neuronal cultures

  • Stroke models (MCAO) with ADORA2B modulation

  • Assessment of excitotoxicity with receptor-specific compounds

• Potential therapeutic applications in stroke and hypoxic-ischemic encephalopathy

These research directions extend our understanding of ADORA2B beyond its established role in axon elongation, highlighting its potential as a therapeutic target in diverse neurological conditions.

How can computational approaches advance ADORA2B research?

Computational methodologies offer powerful tools to accelerate ADORA2B research across multiple dimensions:

Structure-based drug design:

• Homology modeling of chicken and human ADORA2B based on resolved GPCR structures

• Virtual screening of compound libraries for novel modulators

• Molecular dynamics simulations to understand:

  • Receptor activation mechanisms

  • Ligand binding dynamics

  • Conformational changes upon activation

• Integration with experimental validation of top virtual hits

Systems biology approaches:

• Network analysis of ADORA2B signaling pathways

• Multi-scale modeling from molecular to cellular to tissue-level effects

• Prediction of emergent properties from complex ADORA2B signaling networks

• Integration of transcriptomic, proteomic, and metabolomic data

AI and machine learning applications:

• Development of QSAR models for ADORA2B ligand prediction

• Deep learning approaches to predict:

  • Ligand-receptor interactions

  • Off-target effects

  • Pharmacokinetic properties

• Pattern recognition in large datasets to identify novel ADORA2B functions

Evolutionary analysis:

• Phylogenetic studies comparing ADORA2B across species

• Ancestor reconstruction to understand evolutionary constraints

• Positive selection analysis to identify functionally important regions

• Correlation of sequence conservation with structural elements

In silico mutagenesis:

• Computational prediction of effects of ADORA2B mutations

• Energy calculations for receptor stability and ligand binding

• Guide experimental design for targeted mutations

• Building on previous random mutagenesis studies in yeast

Integrative modeling:

• Combine multiple data types (structural, functional, genomic)

• Create predictive models of ADORA2B function in specific contexts

• Simulate effects of receptor modulation in complex systems

• Guide precision medicine approaches for ADORA2B-targeting therapeutics

These computational approaches complement experimental methods using recombinant proteins and can significantly accelerate discovery while reducing resource requirements for ADORA2B research.