Recombinant Bovine P2Y purinoceptor 14 (P2RY14)

What is P2Y purinoceptor 14 and what is its classification?

P2Y purinoceptor 14 (P2RY14) belongs to the P2Y purinoceptor subfamily of G-protein coupled receptors (GPCRs) that respond to nucleotides. Unlike most other purinoceptors that are activated by adenosine diphosphate (ADP) and uridine diphosphate (UDP), P2RY14 is uniquely activated by UDP and UDP-sugars, which act as important signaling molecules in various physiological processes . P2RY14 is classified as a Class A (rhodopsin-like) GPCR featuring the characteristic seven transmembrane spanning regions common to all GPCRs . It plays indispensable roles in multiple biological processes, particularly in immune responses, inflammation, and related disease states including asthma, kidney injury, and lung inflammation .

What are the natural ligands for bovine P2RY14?

The primary endogenous ligands for P2RY14 are UDP-sugars, with UDP-glucose (UDP-Glc) showing the highest potency (EC50=40.3±1.5 nM), followed by UDP-glucuronic acid (UDP-GlcA, EC50=59.9±4.8 nM), UDP-galactose (UDP-Gal, EC50=78.3±9.2 nM), and UDP-N-acetylglucosamine (UDP-GlcNAc, EC50=184.4±11.8 nM) . UDP itself also potently activates P2RY14 with an EC50 of 50.9±6.1 nM . These sugar nucleotides serve as critical signaling molecules via P2RY14 to mediate various physiological processes, with UDP-glucose specifically regulating immune responses associated with inflammatory conditions .

How does P2RY14 signal transduction differ from other purinergic receptors?

P2RY14 signal transduction occurs through a G protein-coupled pathway. While most P2Y receptors activate phospholipase C (PLC) leading to the production of inositol 1,4,5-trisphosphate (IP3) and subsequent Ca2+ release from intracellular stores , P2RY14 has some distinct signaling characteristics. The receptor's activation by UDP-sugars triggers conformational changes, particularly in transmembrane helices 6 and 7, which is similar to the activation mechanism observed in the related receptor P2Y12 . The significant conformational shifts (extracellular part of TM6 shifting over 10 Å and TM7 over 5 Å toward the center of the TM helix bundle) during activation appear to be a common mechanism shared among purinergic receptors .

What key structural motifs determine UDP-sugar recognition by P2RY14?

The most critical structural feature for UDP-sugar recognition in P2RY14 is a conserved salt bridging chain formed by four charged residues known as the KDKE chain (K2.60-D2.64-K7.35-E7.36) . This motif, located between transmembrane helices 2 and 7, is essential for distinguishing different UDP-sugars. Molecular dynamics simulations and functional studies have revealed that UDP-Glc binds to an extracellular pocket consisting of transmembrane helices 2-7 and extracellular loop 2 . The binding involves two distinct sub-pockets: sub-pocket 1 accommodates the uridine group while sub-pocket 2 interacts with the sugar moiety . The glucose moiety in UDP-Glc creates additional interactions with TM2, TM3, TM7, and ECL2 regions of the receptor, enhancing its binding compared to UDP alone .

How do molecular dynamics simulations help understand P2RY14 ligand binding?

Molecular dynamics (MD) simulations provide crucial insights into the dynamic interactions between P2RY14 and its ligands. These computational methods have revealed that:

• UDP-Glc acts as an intramolecular "glue" attaching to TM6 and TM7 to activate P2RY14

• The interactions between sugar moieties and TM7 (particularly residue E278) are essential for receptor activation

• Different UDP-sugars (UDP-Glc, UDP-Gal, UDP-GlcA, and UDP-GlcNAc) bind to the same pocket but with varying interaction patterns

• The KDKE salt bridging chain forms specific interactions with each sugar moiety, explaining the different potencies observed

The methodology typically involves constructing homology models based on crystal structures of related receptors (such as P2Y12), followed by ligand docking using programs like Schrodinger Glide software, and finally running MD simulations to analyze the stability and energy of the protein-ligand complex .

What structural features differentiate P2RY14 from closely related P2Y12?

P2Y12 and P2RY14 share high sequence homology (45.67% amino acid sequence identity) , but they possess distinct ligand selectivity profiles. While P2Y12 is potently activated by ADP and its analogs (like 2MeSADP), P2RY14 responds to UDP and UDP-sugars . Both receptors share the conserved KDKE motif that is crucial for sugar recognition . The ligand binding pockets of both receptors involve similar regions (TM helices and extracellular loops), but the specific residues involved in ligand recognition differ, explaining their distinct pharmacological profiles . Understanding these differences is essential for developing selective ligands for each receptor.

What expression systems are optimal for producing functional recombinant bovine P2RY14?

For functional expression of recombinant bovine P2RY14, researchers should consider these methodological approaches:

• Mammalian expression systems: HEK293 or CHO cell lines typically provide proper post-translational modifications and trafficking of GPCRs

• Baculovirus-insect cell system: Particularly useful for larger-scale protein production with mammalian-like glycosylation patterns

• Yeast expression systems: Can be used for high-throughput screening but may require optimization for proper folding

The expression construct should include:

• A strong promoter (CMV for mammalian cells)

• An N-terminal signal sequence to ensure proper membrane insertion

• A C-terminal epitope tag (FLAG, His6, or HA) for detection and purification

• Codon optimization for the expression host

Validation of functional expression should include both protein detection (Western blotting, immunofluorescence) and functional assays (calcium mobilization, cAMP inhibition, or β-arrestin recruitment) .

What methods are most effective for detecting P2RY14 expression?

Multiple complementary approaches should be employed to verify P2RY14 expression:

• RT-PCR: For detecting P2RY14 mRNA expression using specific primers designed based on published sequences. The methodology involves:

  • RNA extraction from cultured cells

  • cDNA synthesis using reverse transcriptase

  • PCR amplification with P2RY14-specific primers

  • Confirmation by gel electrophoresis and restriction enzyme digestion

• Immunological detection:

  • Western blotting using antibodies against P2RY14 or epitope tags

  • Immunofluorescence microscopy to visualize cellular localization

  • Flow cytometry for quantitative assessment of surface expression

• Functional validation:

  • Calcium mobilization assays using fluorescent indicators like Fura-2

  • Measurement of G-protein activation using [35S]GTPγS binding

  • Monitoring downstream signaling pathways specific to P2RY14 activation

How can the functional activity of recombinant P2RY14 be verified?

Functional validation of recombinant P2RY14 requires multiple assays targeting different aspects of receptor function:

• Ligand binding assays:

  • Competition binding assays using radiolabeled or fluorescent UDP or UDP-glucose

  • Saturation binding to determine Bmax and Kd values

• Signaling assays:

  • Calcium mobilization measurements using Fura-2 loaded cells

  • cAMP inhibition assays (as P2RY14 couples to Gi/o proteins)

  • ERK1/2 phosphorylation detection by Western blotting

• Dose-response relationships:

  • Establishing EC50 values for various ligands (UDP, UDP-Glc, UDP-Gal, UDP-GlcA, UDP-GlcNAc)

  • Comparing the potency order with published data (UDP-Glc > UDP-GlcA > UDP-Gal > UDP-GlcNAc)

• Antagonist sensitivity:

  • Verifying inhibition by known P2RY14 antagonists

  • Demonstrating specificity through lack of response to ligands of other P2Y receptors

How does the KDKE motif distinguish between different UDP-sugars in P2RY14?

The KDKE (K2.60-D2.64-K7.35-E7.36) salt bridging chain in P2RY14 plays a crucial role in discriminating between different UDP-sugars through specific interaction patterns:

• For UDP-Glc: The KDKE chain forms optimal interactions with the glucose moiety, with K77 and E278 making direct contacts with the sugar hydroxyls, resulting in the highest potency (EC50=40.3±1.5 nM)

• For UDP-Gal: Despite being an isomer of UDP-Glc (differing only in the orientation of the C4 hydroxyl group), UDP-Gal shows reduced potency (EC50=78.3±9.2 nM) due to altered interactions with the KDKE chain

• For UDP-GlcA: The carboxyl group at C6 creates modified electrostatic interactions with the KDKE chain, particularly with K77, resulting in intermediate potency (EC50=59.9±4.8 nM)

• For UDP-GlcNAc: The N-acetyl substitution at C2 causes steric hindrance and disrupts optimal interactions with the KDKE chain, leading to the lowest potency (EC50=184.4±11.8 nM)

Molecular dynamics simulations reveal that these differences in interactions with the KDKE chain correlate directly with the observed potency differences, highlighting the critical role of this motif in ligand discrimination .

What are the key considerations in designing selective agonists for P2RY14?

Designing selective agonists for P2RY14 requires understanding the molecular determinants of receptor activation and selectivity:

• Structural requirements:

  • Retention of the UDP core structure

  • Modification of the sugar moiety based on interactions with the KDKE chain

  • Targeting specific residues in sub-pocket 2 that interact with the sugar moiety

• Selectivity considerations:

  • Exploiting differences between P2RY14 and other P2Y receptors, particularly P2Y12

  • Focusing on interactions with residues unique to P2RY14

  • Testing against a panel of P2Y receptors to confirm selectivity

• Rational design approach:

  • Using homology models and MD simulations to predict binding modes

  • Employing structure-activity relationship (SAR) studies

  • Iterative optimization based on functional assay results

• Pharmacokinetic considerations:

  • Addressing the metabolic stability of nucleotide-based compounds

  • Improving membrane permeability by masking charged groups

  • Considering prodrug approaches to improve bioavailability

What methodologies can resolve contradictory findings in P2RY14 signaling studies?

When faced with contradictory findings in P2RY14 signaling studies, consider these methodological approaches:

• Expression system variability:

  • Compare receptor expression levels across different systems using quantitative methods

  • Verify receptor glycosylation and other post-translational modifications

  • Assess the expression of relevant G proteins and downstream effectors

• Assay-specific differences:

  • Employ multiple, complementary functional assays (calcium mobilization, cAMP inhibition, β-arrestin recruitment)

  • Compare real-time vs. endpoint measurements

  • Standardize assay conditions (temperature, buffer composition, cell density)

• Ligand-related considerations:

  • Verify ligand purity and stability

  • Conduct concentration-response studies under identical conditions

  • Consider potential metabolic conversion of ligands

• Detailed mechanistic studies:

  • Use selective G protein inhibitors (pertussis toxin for Gi/o)

  • Apply CRISPR/Cas9 to knockout specific signaling components

  • Employ biased signaling analysis to detect pathway-specific activation

• Computational approaches:

  • Use molecular dynamics simulations to test hypotheses about receptor conformational states

  • Build mathematical models of signaling pathways to predict experimental outcomes

How does P2RY14 function in inflammatory and immune responses?

P2RY14 plays crucial roles in inflammatory and immune responses through several mechanisms:

• Immune cell regulation:

  • P2RY14 activation by UDP-glucose regulates neutrophil recruitment and function

  • Mediates chemotaxis and degranulation in mast cells

  • Modulates dendritic cell maturation and cytokine production

• Inflammatory conditions:

  • Involved in asthmatic inflammation through regulation of airway smooth muscle and immune cell function

  • Participates in kidney injury pathways

  • Contributes to lung inflammation through multiple mechanisms

• Signaling pathways:

  • Activates G proteins (primarily Gi/o) leading to inhibition of adenylyl cyclase

  • Triggers calcium mobilization from intracellular stores

  • Induces MAP kinase pathway activation

Understanding these mechanisms provides valuable insights for developing therapeutic strategies targeting P2RY14 in inflammatory diseases and immune disorders.

What experimental models are most appropriate for studying P2RY14 in disease states?

When investigating P2RY14 in disease contexts, several experimental models prove valuable:

• Cell culture models:

  • Primary immune cells (neutrophils, macrophages, dendritic cells)

  • Airway epithelial cells for respiratory inflammation

  • Renal tubular epithelial cells for kidney injury models

• Ex vivo tissue preparations:

  • Precision-cut lung slices for respiratory studies

  • Isolated perfused kidney for renal investigations

  • Intestinal organoids for gastrointestinal research

• Animal models:

  • P2RY14 knockout mice to assess receptor function in disease contexts

  • Inducible, tissue-specific knockout models to dissect cell-specific roles

  • Disease-specific models (OVA-induced asthma, LPS-induced inflammation, ischemia-reperfusion injury)

• Methodological considerations:

  • Use multiple disease models to ensure robust findings

  • Employ both pharmacological (antagonists) and genetic (knockout) approaches

  • Validate findings in human samples when possible

What are the challenges in translating P2RY14 research to therapeutic applications?

Translating P2RY14 research into therapeutic applications faces several methodological challenges:

• Ligand development issues:

  • Poor pharmacokinetic properties of nucleotide-based compounds

  • Difficulty in achieving selectivity against related P2Y receptors

  • Limited blood-brain barrier penetration for CNS indications

• Target validation considerations:

  • Potential compensatory mechanisms in chronic antagonism

  • Species differences in receptor pharmacology between experimental models and humans

  • Context-dependent signaling in different tissues and disease states

• Experimental design recommendations:

  • Establish clear target engagement biomarkers

  • Develop tissue-specific delivery strategies

  • Design dual-targeting approaches (e.g., targeting P2RY14 and complementary inflammatory pathways)

• Clinical translation approaches:

  • Focus initial studies on diseases with strong preclinical evidence (respiratory inflammation, kidney injury)

  • Consider biomarker-guided patient selection

  • Design early clinical studies with pharmacodynamic endpoints to confirm mechanism