Recombinant Guinea pig Cysteinyl leukotriene receptor 1 (CYSLTR1)

What is the structure and amino acid sequence of recombinant Guinea pig CYSLTR1?

Recombinant Full Length Guinea pig Cysteinyl leukotriene receptor 1 (CYSLTR1) protein (Q2NNR5) consists of 340 amino acids. The complete sequence is:

MDETGNPTIPPASNNTCYDSIDDFRNQVYSTLYSMISVVGFFGNGFVLYVLVKTYHEKSAFQVYMINLAVADLLCVCTLPLRVAYYVHKGIWLFGDFLCRLSTYALYVNLYCSIFFMTAMSFFRCVAIVFPVQNISLVTQKKARLVCIAIWMFVILTSSPFLMANTYKDEKNNTKCFEPPQDNQAKNYVLILHYVSLFIGFIIPFITIIVCYTMIIFTLLKSSMKKNLSSRKRAIGMIIVVTAAFLVSFMPYHIQRTIHLHFLHNKTKPCDSILRMQKSVVITLSLAASNCCFDPLLYFFSGGNFRRRLSTIRKYSLSSMTYIPKKKTSLPQKGKDICKE

The protein is typically expressed with an N-terminal His-tag in E. coli expression systems for research applications. The protein belongs to the G-protein-coupled receptor family and contains characteristic transmembrane domains necessary for its function in signaling pathways.

What are the optimal storage and handling conditions for recombinant Guinea pig CYSLTR1?

For maximum stability and activity preservation of recombinant Guinea pig CYSLTR1:

Upon reconstitution, brief centrifugation is recommended prior to opening to bring the contents to the bottom of the vial. The default final concentration of glycerol is typically 50% for optimal preservation .

How can researchers verify the purity and functionality of recombinant Guinea pig CYSLTR1?

Several complementary methods can be employed to verify protein quality:

• SDS-PAGE analysis: The recombinant protein should show greater than 90% purity by SDS-PAGE, appearing as a predominant band at the expected molecular weight .

• Western blotting: Using anti-His antibodies can confirm the presence of the His-tagged protein.

• Ligand binding assays: Functional verification through radioligand binding assays using known CYSLTR1 ligands like LTD4.

• Calcium mobilization assays: Measuring intracellular calcium increases in response to agonist stimulation in cells expressing the receptor.

• Receptor antagonist studies: Verifying that known CYSLTR1 antagonists (such as montelukast) can block functional responses in appropriate assay systems .

How can researchers develop effective anaphylaxis models using Guinea pig CYSLTR1?

A novel model utilizing S-hexyl GSH has been developed that allows researchers to study both CYSLTR1 and CYSLTR2-mediated anaphylaxis:

• Animal preparation: Active sensitization of guinea pigs followed by challenge with OVA (ovalbumin).

• Metabolic manipulation: Application of S-hexyl GSH, a γ-glutamyl transpeptidase (GTP) inhibitor, to suppress conversion of LTC4 to LTD4.

• Receptor antagonism studies:

  • Without S-hexyl GSH: OVA-induced fatal anaphylaxis is almost completely inhibited by montelukast (CYSLTR1 antagonist), but not by BayCysLT2RA (CYSLTR2 antagonist).

  • With S-hexyl GSH: The inhibitory effect of montelukast is dramatically diminished, while that of BayCysLT2RA is markedly increased.

  • Dual antagonists (ONO-6950) effectively inhibit anaphylactic responses in both conditions.

• Verification of metabolic inhibition: LC/MS/MS analysis can confirm that S-hexyl GSH treatment inhibits LTC4 metabolism in blood and lung tissues .

This model provides a valuable platform for screening both CYSLTR2 and CYSLTR1/2 receptor antagonists and for functional analysis of these receptors.

What methods are effective for studying CYSLTR1 desensitization and trafficking?

Researchers can employ several approaches to investigate the complex mechanisms of CYSLTR1 desensitization and trafficking:

• Homologous vs. heterologous desensitization:

  • Exposure to LTD4 (cognate ligand) induces rapid homologous desensitization of CYSLTR1.

  • Activation of P2Y receptors with ATP or UDP induces heterologous desensitization of CYSLTR1.

  • Interestingly, LTD4-induced CYSLTR1 activation has no effect on P2Y receptor responses, suggesting a hierarchy in desensitizing signals .

• Monitoring techniques:

  • Measure reduction in maximal agonist-induced intracellular cytosolic Ca2+ transients.

  • Assess receptor internalization using equilibrium binding assays and confocal microscopy.

• Differential recovery mechanisms:

  • ATP/UDP-induced CYSLTR1 desensitization does not cause receptor internalization.

  • Heterologous desensitization allows faster recovery of CYSLTR1 functionality.

  • Homologous desensitization, likely dependent upon G-protein-receptor kinase 2, induces faster receptor downregulation and slower functional recovery .

• Signaling pathway investigation:

  • Heterologous desensitization is dependent upon protein kinase C.

  • Different kinase inhibitors can help distinguish between pathways involved in homologous versus heterologous desensitization.

How do CYSLTR1 and CYSLTR2 receptors differ functionally in Guinea pig models?

Guinea pig models reveal distinct functional profiles for these receptor subtypes:

These functional differences provide valuable tools for dissecting the specific contributions of each receptor subtype in physiological and pathological processes .

What evidence suggests the existence of additional CysLT receptor subtypes beyond CYSLTR1 and CYSLTR2?

Several pharmacological observations point to the potential existence of additional receptor subtypes (possibly CYSLTR3):

• Tissue-specific responses: In guinea pig tissues, there is significant variability in antagonist potency, with the ileum being most susceptible to blockade, while the trachea and particularly the lung parenchyma require considerably higher concentrations of antagonists .

• Incomplete antagonism: The contraction response to LTD4 in guinea pig lung parenchyma is poorly inhibited by both potent CYSLTR1 antagonists (such as ICI-198,615) and by combined CYSLTR1/CYSLTR2 antagonists (such as BAY u9773) .

• Species differences: Significant differences exist in the potency of selective CYSLTR1 antagonists between rat lung and guinea pig trachea, which may reflect species-specific receptor subtypes .

• Metabolic conversion effects: When the metabolic conversion of LTC4 into LTD4 was arrested in guinea pig trachea, it was observed that LTC4 could not be antagonized by certain antagonists, suggesting distinctive receptor pharmacology .

These observations collectively suggest a more complex receptor classification system that may include additional subtypes beyond the conventional CYSLTR1/CYSLTR2 categorization.

How does cross-talk between CYSLTR1 and P2Y receptors affect inflammatory responses?

The relationship between CYSLTR1 and P2Y receptors represents an important regulatory mechanism at sites of inflammation:

• Hierarchical desensitization: Activation of P2Y receptors with ATP or UDP induces heterologous desensitization of the CYSLTR1 receptor. Conversely, LTD4-induced CYSLTR1 activation has no effect on P2Y receptor responses, suggesting a one-way regulatory relationship .

• Differential receptor trafficking: Unlike homologous desensitization, ATP/UDP-induced CYSLTR1 desensitization does not cause receptor internalization, allowing faster recovery of CYSLTR1 functionality .

• Distinct signaling pathways: Heterologous desensitization is dependent upon protein kinase C, while homologous desensitization likely depends on G-protein-receptor kinase 2 activation .

• Physiological implications: This cross-regulation may serve as a feedback mechanism at sites of inflammation where both cysteinyl-leukotrienes and extracellular nucleotides accumulate, allowing cells to fine-tune their responses to multiple inflammatory mediators .

• Potential therapeutic targets: Understanding this cross-talk provides insight into developing more effective anti-inflammatory strategies targeting multiple receptor systems simultaneously.

What methodological approaches best elucidate Guinea pig CYSLTR1 coupling to G proteins?

Several experimental approaches can help characterize G-protein coupling to Guinea pig CYSLTR1:

• Recombinant expression systems: When expressed in recombinant systems, CysLT1 and CysLT2 receptors can couple to distinct types of G proteins, allowing isolation and characterization of specific coupling preferences .

• GTPγS binding assays: These measure the exchange of GDP for GTPγS on the G protein α-subunit following receptor activation.

• Intracellular signaling readouts: Measuring specific downstream effectors such as:

  • Calcium mobilization from intracellular stores (Gq coupling)

  • cAMP production (Gs coupling) or inhibition (Gi coupling)

  • Activation of small GTPases (G12/13 coupling)

• Receptor mutagenesis: Targeted mutations in intracellular loops and C-terminal domains can identify regions critical for specific G-protein interactions.

• Pertussis toxin sensitivity: Determining if responses are inhibited by pertussis toxin helps identify Gi/o coupling.

How can researchers effectively use Guinea pig CYSLTR1 models in drug discovery?

Guinea pig CYSLTR1 models offer several advantages for drug discovery applications:

• Anaphylaxis model with S-hexyl GSH: This model allows screening of both CYSLTR1 and CYSLTR2 receptor antagonists by manipulating the metabolic conversion of leukotrienes .

• Tissue-specific pharmacology: The different sensitivity of various guinea pig tissues (ileum, trachea, lung parenchyma) to CYSLTR1 antagonists enables comprehensive profiling of drug candidates .

• Cross-species comparison: Significant differences in antagonist potency between species help predict potential translational challenges in drug development .

• Dual and selective antagonism: Testing compounds against both selective targets (montelukast for CYSLTR1, BayCysLT2RA for CYSLTR2) and dual targets (ONO-6950) allows comprehensive pharmacological characterization .

• Crosstalk investigation: Models examining CYSLTR1 and P2Y receptor interactions can help develop strategies targeting multiple inflammatory pathways simultaneously .

What are the challenges in translating Guinea pig CYSLTR1 research to human applications?

Several important considerations affect translational research:

• Species differences: Significant variations exist in antagonist potency between species, requiring careful extrapolation of findings .

• Receptor subtype distribution: The distribution and density of receptor subtypes may differ between guinea pigs and humans across tissues.

• Signaling pathway variations: While core signaling mechanisms may be conserved, species-specific differences in effector coupling and regulatory pathways can affect drug responses.

• Model limitations: Guinea pig models may not fully recapitulate the complex pathophysiology of human diseases like asthma or other inflammatory conditions.

• Genetic and molecular tools: Fewer genetic and molecular tools are available for guinea pig research compared to mouse models, limiting certain mechanistic investigations.

Despite these challenges, guinea pig models remain valuable for respiratory and inflammatory research due to their physiological similarities to humans, particularly in airway responses to inflammatory mediators.