Recombinant Rat Taste receptor type 2 member 117 (Tas2r117)

What is Tas2r117 and what is its role in rat sensory systems?

Tas2r117 is a bitter taste receptor belonging to the taste receptor type 2 (T2R) family, also known as T2R39. It functions as a G protein-coupled receptor involved in bitter taste perception. The receptor has a full sequence of 318 amino acids and is encoded by the Tas2r117 gene (synonyms: T2r39). The protein consists of specific domains that contribute to its ability to detect bitter compounds and trigger downstream signaling cascades. Beyond taste perception, emerging research suggests Tas2r117 may have extraoral functions, particularly in the respiratory and gastrointestinal systems .

How is recombinant Tas2r117 typically produced for research applications?

Recombinant Tas2r117 protein is generally produced using mammalian, insect, or bacterial expression systems. For optimal functionality, mammalian expression systems (typically HEK293 or CHO cells) are preferred as they provide proper post-translational modifications. The protein is often expressed with tags (such as His, GST, or Fc) to facilitate purification, which is typically achieved through affinity chromatography. The purified protein is then stored in a Tris-based buffer with 50% glycerol for stability. For experimental use, storage at -20°C is recommended, with extended storage at -80°C. Repeated freeze-thaw cycles should be avoided, and working aliquots should be maintained at 4°C for up to one week to maintain protein integrity .

How does Tas2r117 expression and function differ across tissues beyond the oral cavity?

While initially characterized in taste buds, Tas2r117 shows significant extraoral expression patterns that suggest broader physiological roles. Research indicates expression in the respiratory tract, particularly in alveolar macrophages where it may participate in inflammatory responses. The receptor has also been identified in the gastrointestinal tract, particularly in enteroendocrine cells, where it appears to mediate responses to bitter compounds that can affect hormone secretion and food intake regulation .

In the respiratory system, Tas2r117 and related bitter taste receptors may participate in sensing bacterial products and initiating immune responses. In the gastrointestinal tract, activation of these receptors can stimulate the release of gut hormones, including GLP-1 and PYY, which regulate appetite and glucose metabolism. These tissue-specific functions suggest that Tas2r117 has evolved beyond its classical role in taste perception to serve as part of broader chemosensory systems throughout the body .

What signaling pathways are associated with Tas2r117 activation in different cell types?

Tas2r117 activation triggers distinct signaling cascades depending on the cellular context:

In taste cells, the classical pathway involves gustducin activation, leading to increased intracellular calcium and neurotransmitter release. In enteroendocrine cells, Tas2r117 activation can modulate the release of hormones that regulate appetite and digestive functions. In alveolar macrophages, there appears to be crosstalk between Tas2r117 signaling and immune response pathways, potentially involving the Aryl hydrocarbon Receptor (AhR) and NF-κB regulation. These diverse signaling mechanisms underlie the pleiotropic effects of Tas2r117 in different physiological contexts .

How do flavanols and polyphenols interact with Tas2r117 to modulate enteroendocrine function?

Flavanols and other polyphenols can act as ligands for Tas2r117 and related bitter taste receptors in the gastrointestinal tract. Research has shown that grape-seed proanthocyanidin extract (GSPE) and other flavanol-rich compounds can stimulate the enteroendocrine system through TAS2R activation. This interaction leads to the secretion of gut hormones, particularly GLP-1 and PYY, which play roles in appetite suppression and glucose homeostasis .

The mechanism involves:

• Direct binding of polyphenolic compounds to Tas2r117 on enteroendocrine cells

• Activation of intracellular signaling cascades

• Increased calcium mobilization

• Stimulation of hormone secretion

• Subsequent effects on pancreatic function and appetite regulation

Interestingly, the effects appear to be location-dependent within the gastrointestinal tract, with differential responses in the proximal versus distal gut. Some studies suggest that GLP-1 and PYY can be secreted and act within the intestinal lumen of the human colon, indicating complex paracrine signaling mechanisms in addition to their endocrine functions .

What are the optimal conditions for handling and storing Recombinant Rat Tas2r117 protein?

For experimental applications, it is advisable to prepare small working aliquots to minimize freeze-thaw cycles. The protein should be handled on ice when thawed, and centrifuged briefly before opening to ensure all contents are at the bottom of the tube. For functional assays, the buffer components should be compatible with the experimental system, as some buffer components may interfere with certain assays .

What cell models are most appropriate for studying Tas2r117 function in different physiological contexts?

For enteroendocrine studies, both in vitro cell lines and ex vivo intestinal samples have provided valuable insights. The choice depends on the specific research question, with cell lines offering greater control and reproducibility, while ex vivo systems better recapitulate the physiological environment. For respiratory studies, alveolar macrophage models can be used to examine Tas2r117's role in inflammatory responses and bacterial signal sensing .

What are the current methodologies for measuring Tas2r117 activation in experimental settings?

Several complementary techniques can be employed to assess Tas2r117 activation:

• Calcium Mobilization Assays:

  • Fluorescent calcium indicators (Fluo-4, Fura-2)

  • Genetically encoded calcium indicators (GCaMP)

  • Provides real-time measurement of receptor activation

• Receptor Internalization:

  • Fluorescently tagged Tas2r117

  • Immunocytochemistry

  • Quantifies receptor trafficking following activation

• Downstream Signaling:

  • cAMP assays

  • IP3 measurements

  • ERK phosphorylation

  • Assess specific pathway activation

• Functional Readouts:

  • Hormone secretion assays (ELISA for GLP-1, PYY)

  • Gene expression analysis (qPCR for early response genes)

  • Cell-specific functional changes (e.g., macrophage polarization)

These methods can be combined for comprehensive characterization of receptor activation and signaling. For example, calcium imaging can be paired with hormone secretion assays to correlate receptor activation with functional outcomes in enteroendocrine cells .

How can researchers distinguish between direct and indirect effects of compounds on Tas2r117 activation?

Distinguishing direct from indirect effects requires a systematic approach:

• Direct Binding Studies:

  • Radioligand binding assays with purified Tas2r117

  • Surface plasmon resonance (SPR)

  • Microscale thermophoresis (MST)

  • These provide evidence of direct physical interaction

• Molecular Docking and Modeling:

  • In silico prediction of ligand-receptor interactions

  • Structure-activity relationship (SAR) analysis

  • Helps identify key binding residues

• Genetic Approaches:

  • Receptor knockout or knockdown systems

  • Site-directed mutagenesis of putative binding sites

  • Tests necessity of the receptor for observed effects

• Pharmacological Approaches:

  • Specific antagonists or allosteric modulators

  • Dose-response relationships

  • Competition assays

• Temporal Analysis:

  • Rapid responses (seconds to minutes) suggest direct activation

  • Delayed responses may indicate indirect mechanisms

A comprehensive approach combining multiple methods provides the strongest evidence for direct versus indirect effects. For example, a compound showing binding in biochemical assays, predictable structure-activity relationships, and loss of activity in receptor knockout models would strongly support direct Tas2r117 activation .

What are the emerging correlations between Tas2r117 activation and inflammatory responses in the respiratory system?

Research indicates complex relationships between Tas2r117 activation and inflammatory processes:

These seemingly contradictory findings suggest context-dependent effects, where Tas2r117 activation may initially promote inflammatory responses but subsequently contribute to resolution phases. The data indicate that D-Tryptophan, a potential Tas2r117 ligand, can reduce neutrophil recruitment after acute lung injury and modulate macrophage polarization in an AhR-dependent manner. This suggests therapeutic potential in respiratory inflammatory conditions, where the timing and concentration of receptor activation may be critical determinants of the physiological outcome .

How do the functions of Tas2r117 compare with other TAS2R family members in different physiological systems?

Comparative analysis of TAS2R family members reveals diverse functions across systems:

Functional genomic studies have provided insights into the evolutionary and functional relationships among TAS2R family members. While all function as bitter taste sensors, they display different ligand specificities and expression patterns that correlate with diverse physiological roles. Some, like human TAS2R5, appear particularly important in regulating food intake through interaction with dietary components like flavanols and polyphenols. The selective stimulation of specific TAS2R members can lead to differential physiological outcomes, suggesting potential for targeted therapeutic approaches .

What are the therapeutic implications of targeting Tas2r117 in inflammatory respiratory conditions?

The immunomodulatory effects of Tas2r117 activation, particularly by compounds like D-tryptophan, suggest significant therapeutic potential for inflammatory respiratory conditions. Research indicates that D-tryptophan treatment can reduce neutrophil recruitment following acute lung injury and modulate inflammatory cytokine production in alveolar macrophages through AhR-dependent mechanisms .

Key therapeutic implications include:

• Anti-inflammatory Applications:

  • Potential to reduce neutrophilic inflammation in acute lung injury

  • Modulation of alveolar macrophage polarization toward anti-inflammatory phenotypes

  • Reduction of pro-inflammatory cytokine production

• Resolution-Promoting Effects:

  • Enhancement of M2 macrophage polarization supporting tissue repair

  • Potential acceleration of inflammatory resolution phases

  • Support for homeostatic recovery mechanisms

• Bacterial Signal Sensing:

  • Potential role in detecting bacterial metabolites

  • Possible adjunctive therapy to conventional antibiotics

  • Enhancement of host defense mechanisms

Future research should focus on optimizing delivery methods, determining effective dosing regimens, and identifying specific Tas2r117 ligands with selective activities. The receptor-specific nature of these effects suggests the potential for precise therapeutic targeting with minimal off-target effects .

How might Tas2r117 and related TAS2Rs be exploited for managing metabolic disorders through enteroendocrine modulation?

The involvement of Tas2r117 and related TAS2Rs in enteroendocrine function presents opportunities for metabolic disorder management:

Research has shown that grape-seed proanthocyanidin extract (GSPE) and other flavanols can stimulate the enteroendocrine system through TAS2R activation, leading to hormone secretions that influence both appetite and pancreatic function. Notably, glucagon appears more sensitive than insulin to GSPE treatment, correlating with enhanced ileal GLP-1 secretion .

The selective targeting of specific TAS2R members offers a nuanced approach to metabolic regulation, as different receptors may induce distinct patterns of hormone secretion. This selective stimulation capability provides a potential mechanism for either increasing or reducing food intake based on which receptors are targeted, suggesting personalized approaches for different metabolic conditions .

What technical challenges must be overcome to advance Tas2r117 research and therapeutic applications?

A significant challenge in advancing Tas2r117 research is the limited structural information available for this receptor family. While amino acid sequences are known, detailed three-dimensional structures would facilitate rational drug design. Additionally, developing selective agonists and antagonists that can discriminate between closely related TAS2R family members would enable more precise experimental and therapeutic approaches.

For translational applications, understanding species differences in receptor pharmacology is essential, as rat Tas2r117 may differ from its human ortholog in ligand specificity and signaling properties. Developing appropriate model systems, including humanized animal models and human tissue-derived organoids, will be crucial for advancing potential therapeutic applications .