Recombinant Gorilla gorilla gorilla Taste receptor type 2 member 13 (TAS2R13)

What is the evolutionary significance of TAS2R13 in western lowland gorillas (Gorilla gorilla gorilla)?

TAS2R13 belongs to the broader family of bitter taste receptors (TAS2Rs) that have significant evolutionary importance across primates. Bitter taste receptors in gorillas, like other great apes, show evidence of being under selection pressure, likely due to their essential role in detecting potentially toxic compounds in their diet. Similar to other TAS2R genes found in eastern gorillas (such as TAS2R14), TAS2R13 may have undergone selection related to dietary adaptations . Western lowland gorillas are primarily frugivorous, which contrasts with the more herbaceous diets of eastern gorillas, potentially driving different selective pressures on their taste receptor genes .

How does recombinant TAS2R13 expression compare between gorillas and other great apes?

Recombinant expression studies with gorilla TAS2R genes, similar to those conducted with human and chimpanzee TAS2Rs, show variable expression efficiencies. In comparable studies with other TAS2R genes, expression rates typically range between 3-20% of transfected cells . The localization patterns may vary between different receptors, with some showing more pronounced expression at the plasma membrane and others expressing more at the intracellular level. When designing recombinant expression studies for gorilla TAS2R13, researchers should anticipate similar variability and optimize transfection protocols accordingly .

What are the standard methods for functional characterization of recombinant gorilla TAS2R13?

Functional characterization of recombinant gorilla TAS2R13 typically involves:

• Gene synthesis and restoration of the open reading frame if necessary

• Transfection into a heterologous expression system (commonly HEK293T cells)

• Verification of expression using epitope tags (such as HSV glycoprotein D)

• Calcium imaging assays to measure receptor activation upon compound exposure

• Dose-response experiments to determine receptor sensitivity to identified agonists

This approach parallels methods used for other primate TAS2Rs where cells are transiently transfected with the receptor construct and a coupling chimeric G protein to enable measurement of intracellular calcium signals upon receptor activation .

How should researchers design agonist screening protocols for recombinant gorilla TAS2R13?

When designing agonist screening protocols for recombinant gorilla TAS2R13, researchers should implement a comprehensive approach that reflects the receptor's biological context:

Recommended Screening Protocol:

• Compound selection: Include a diverse library of bitter compounds (minimum 80-100) representing various chemical classes present in plants from gorilla habitats .

• Concentration ranges: Begin with higher concentrations (100-300 µM) for initial screening, followed by dose-response curves (typically 0.1-1000 µM) for positive hits.

• Controls: Include compounds known to activate related TAS2Rs in other primates as positive controls.

• Cross-species comparison: Test the same compound library against human and chimpanzee orthologs to identify species-specific differences in agonist recognition.

• Data analysis: Calculate EC50 values for active compounds and determine threshold concentrations for receptor activation.

Based on studies with other TAS2R receptors, expect a relatively narrow tuning profile with approximately 5% of tested compounds activating the receptor . Species-specific activation patterns may reveal important evolutionary adaptations related to diet.

What genetic engineering approaches are most effective for expressing functional recombinant gorilla TAS2R13?

Effective genetic engineering approaches for expressing functional recombinant gorilla TAS2R13 include:

Recommended Genetic Engineering Strategy:

• Vector selection: Use mammalian expression vectors with strong promoters (CMV) and appropriate selection markers.

• Codon optimization: Optimize codons for expression in the selected host cell line to improve protein yield.

• N-terminal tagging: Include an N-terminal epitope tag (such as HSV) for detection without interfering with signaling function .

• Signal sequence modification: Enhance membrane trafficking by incorporating a well-characterized signal sequence if expression is poor.

• Chimeric constructs: For difficult-to-express receptors, create chimeric constructs with well-expressed TAS2R transmembrane domains.

• Co-expression systems: Co-express with chaperone proteins to improve folding and trafficking to the cell membrane.

These approaches should be combined with rigorous quality control to verify proper expression, localization, and functionality of the recombinant receptor .

How can researchers accurately determine the divergence time and evolutionary history of gorilla TAS2R13?

To accurately determine the divergence time and evolutionary history of gorilla TAS2R13, researchers should employ a multi-faceted approach:

Recommended Evolutionary Analysis Protocol:

This comprehensive approach allows researchers to distinguish between neutral evolution, balancing selection, and directional selection, while identifying possible introgression events that may have influenced TAS2R13 evolution in gorillas.

What are the key considerations for designing in vitro expression systems for gorilla TAS2R13?

When designing in vitro expression systems for gorilla TAS2R13, researchers should address several critical factors:

Critical Design Considerations:

• Cell line selection: HEK293T cells are commonly used for TAS2R expression, but alternatives like CHO cells may provide different expression characteristics.

• Expression efficiency monitoring: Include fluorescent markers (e.g., GFP) to track transfection efficiency.

• Membrane localization verification: Use plasma membrane markers (e.g., ConA) alongside receptor labeling to confirm proper localization .

• G-protein coupling: Co-express appropriate G-protein subunits to ensure functional coupling; chimeric G-proteins (Gα16gust44) can enhance signaling.

• Calcium flux measurement: Optimize calcium indicator dye loading and measurement parameters based on expected response kinetics.

• Temperature conditions: Test expression at different temperatures (33°C vs. 37°C) which can affect receptor trafficking.

Based on studies with related TAS2Rs, expect expression rates between 3-20% of transfected cells, with potentially significant variability between experiments . Rigorous controls should be included to account for this variability.

How should researchers account for potential post-translational modifications in recombinant gorilla TAS2R13?

Post-translational modifications significantly impact receptor function and require careful consideration:

Recommended Protocol for Addressing Post-translational Modifications:

• N-glycosylation analysis: Identify potential N-glycosylation sites in gorilla TAS2R13 and test their functional relevance through site-directed mutagenesis.

• Phosphorylation assessment: Examine putative phosphorylation sites in the intracellular domains that may regulate receptor desensitization.

• Palmitoylation evaluation: Investigate potential palmitoylation sites that might affect membrane anchoring and receptor stability.

• Expression system selection: Consider using mammalian expression systems that more accurately recapitulate natural post-translational processing.

• Comparative analysis: Compare post-translational modification patterns between gorilla TAS2R13 and human/chimpanzee orthologs to identify species-specific differences.

These modifications can significantly impact receptor localization, stability, and function, potentially explaining species-specific differences in receptor activity observed between primates .

What controls should be included when evaluating ligand specificity of recombinant gorilla TAS2R13?

Rigorous controls are essential for valid ligand specificity evaluation:

Essential Controls for Ligand Specificity Testing:

• Non-transfected cell controls: Test all compounds on non-transfected cells to identify non-specific cellular responses.

• Mock-transfected controls: Include cells transfected with empty vector to control for transfection effects.

• Positive receptor controls: Co-test well-characterized TAS2Rs with known ligands to confirm assay functionality.

• Cross-receptor testing: Test potential TAS2R13 ligands against other gorilla TAS2Rs to determine specificity.

• Vehicle controls: Test solvent vehicles (DMSO, ethanol) at matching concentrations used for compound delivery.

• Species comparison controls: Test the same compounds on human and chimpanzee TAS2R13 orthologs under identical conditions .

• Dose-response validation: Confirm positive hits with full dose-response curves to distinguish true from false positives.

These controls help distinguish true receptor-specific responses from artifacts and allow for valid cross-species comparisons of receptor function .

How should researchers interpret differences in agonist responses between gorilla TAS2R13 and orthologous receptors in other primates?

Interpreting differences in agonist responses requires careful consideration of multiple factors:

Interpretation Framework:

• Sequence determinants: Map agonist response differences to specific sequence variations between species, focusing on transmembrane domains and extracellular loops likely involved in ligand binding.

• Ecological context: Correlate activation pattern differences with dietary specializations - western lowland gorillas are primarily frugivorous compared to more herbaceous diets of eastern gorillas .

• Evolutionary analysis: Apply selection tests (Tajima's D, HKA, Li's MFDM) to determine if differences reflect neutral evolution or selection .

• Homology modeling: Create structural models to predict how amino acid substitutions affect ligand binding pocket architecture.

• Receptor sensitivity comparison: Compare EC50 values for shared agonists to determine if differences are quantitative (affinity) or qualitative (specificity).

Research with other TAS2R receptors has shown that even closely related species can exhibit differential activation patterns, with some compounds activating receptors from only one species, highlighting the evolutionary dynamism of these receptors .

What statistical approaches should be used to analyze gorilla TAS2R13 population genetics data?

For robust population genetic analysis of gorilla TAS2R13:

Recommended Statistical Framework:

These approaches allow researchers to distinguish between neutral evolution, different forms of selection, and complex demographic scenarios like introgression from extinct lineages .

How can researchers resolve contradictory data between in vitro and in silico predictions for gorilla TAS2R13 function?

When faced with contradictory data between experimental results and computational predictions:

Resolution Strategy:

• Validation through multiple methods:

  • Test predictions using additional experimental approaches (e.g., site-directed mutagenesis, competitive binding assays)

  • Apply alternative computational algorithms and compare results

• Molecular dynamic simulations:

  • Perform simulations of receptor-ligand interactions to understand structural dynamics not captured by static models

  • Include explicit membrane environments in simulations to better approximate natural conditions

• Experimental condition optimization:

  • Test receptor function under various conditions (pH, temperature, ionic concentrations)

  • Evaluate potential allosteric modulators that might explain discrepancies

• Sequence context evaluation:

  • Examine whether specific sequence contexts of gorilla TAS2R13 might affect experimental expression systems

  • Consider creating chimeric receptors to isolate regions causing discrepancies

• Negative results publication:

  • Document contradictory findings transparently to contribute to the field's understanding

  • Propose testable hypotheses that might explain the observed discrepancies

This methodical approach helps resolve contradictions and can lead to novel insights about receptor function that neither approach alone would reveal.

How does gorilla TAS2R13 function relate to dietary adaptation and toxin avoidance in wild populations?

The relationship between TAS2R13 function and gorilla dietary ecology:

Key Ecological Relationships:

• Diet composition correlation:

  • Western lowland gorillas (Gorilla gorilla gorilla) consume more fruit than eastern gorillas, potentially requiring different bitter perception profiles

  • Seasonal variation in diet may correspond to polymorphisms in TAS2R genes that allow for flexible responses to different plant compound profiles

• Toxic compound detection:

  • TAS2R receptors evolved primarily to detect potentially harmful compounds in plant foods

  • Like TAS2R14 (identified as a target of selection in gorillas), TAS2R13 may detect specific classes of toxic compounds relevant to gorilla diets

• Geographic variation:

  • Different gorilla populations encounter different plant species with varying bitter compound profiles

  • Population-specific adaptations in TAS2R13 may correlate with local plant biodiversity

• Functional ecology:

  • Comparative activation patterns of recombinant TAS2R13 by compounds from plants in gorilla habitats can reveal ecological relevance

  • Threshold concentrations for activation may correspond to natural concentrations in food plants

• Behavioral studies integration:

  • Correlation between TAS2R13 genotypes and observed feeding preferences in wild gorillas

  • Food choice tests with captive gorillas of known TAS2R13 genotypes may reveal functional relevance

Understanding these relationships provides insights into how sensory perception shapes dietary niche and ultimately influences fitness in wild gorilla populations .

What evidence suggests adaptive introgression has affected gorilla TAS2R13 evolution?

Evaluating potential adaptive introgression in gorilla TAS2R13:

Introgression Evidence Framework:

• Genomic signatures of introgression:

  • Apply S* statistic analysis to detect highly divergent genomic windows relative to outgroups

  • Use hmmix method to identify regions with unusual patterns of private mutations

• Selection tests on introgressed regions:

  • Apply VolcanoFinder to detect distorted site frequency spectra consistent with selective sweeps around introgressed alleles

  • Compare with patterns observed in other bitter taste receptor genes (e.g., TAS2R14) identified as targets of adaptive introgression

• Divergence dating:

  • Estimate divergence times between variants to identify unusually divergent haplotypes

  • Compare with expected coalescence times under standard demographic models

• Functional impact assessment:

  • Identify protein-coding changes in putatively introgressed regions

  • Test whether variants in these regions alter receptor function or specificity

• Comparative analysis with other great apes:

  • Examine if similar patterns exist in other ape species with distinct dietary adaptations

  • Consider whether shared selective pressures might lead to convergent evolution rather than introgression

The discovery of ghost admixture in eastern gorillas (~16.4% of the autosomal genome) suggests that similar processes may have affected TAS2R genes in western gorillas, potentially including TAS2R13 .

How do pseudogenization events in primate TAS2R genes inform our understanding of gorilla TAS2R13 function?

Pseudogenization events provide important evolutionary context:

Pseudogenization Insights:

• Species-specific pseudogenes:

  • Related human TAS2R pseudogenes (TAS2R2, TAS2R62, TAS2R64) show evidence of functionality in recent evolutionary history

  • These genes remain functional in chimpanzees, suggesting independent pseudogenization events in human lineage

• Ancient balancing selection:

  • Evidence of balancing selection prior to pseudogenization events (positive Tajima's D values, significant HKA test results) in related TAS2R genes

  • This suggests functional importance before loss of function occurred

• Polymorphic pseudogenization:

  • Some TAS2R genes show evidence of being functional in some ancient hominin populations (e.g., Denisovan) but pseudogenized in others (e.g., Neanderthal)

  • This suggests that TAS2R13 functionality may vary across gorilla populations

• Compensatory mechanisms:

  • When one TAS2R is pseudogenized, other receptors may compensate through broader agonist profiles

  • Functional redundancy among TAS2R family members may allow some receptors to be lost without significant fitness costs

• Dating pseudogenization events:

  • Molecular clock analyses can date when pseudogenization occurred

  • Correlation with environmental or dietary shifts may reveal selective pressures

These patterns suggest that bitter taste receptor repertoires are dynamically evolving in response to changing environmental challenges, with some receptors being expendable under certain ecological conditions .

What are the most effective heterologous expression systems for functional studies of gorilla TAS2R13?

Selecting optimal expression systems for functional studies:

Expression System Comparison:

Selection should be based on specific research goals, with HEK293T cells being the standard for initial characterization and specialized systems for more detailed functional analyses .

How can site-directed mutagenesis reveal structure-function relationships in gorilla TAS2R13?

Strategic application of site-directed mutagenesis:

Mutagenesis Approach:

• Key target regions:

  • Transmembrane domains predicted to form the binding pocket

  • Extracellular loops involved in ligand entry

  • Intracellular regions critical for G-protein coupling

  • Species-specific amino acid differences between gorilla and other primates

• Mutation types to consider:

  • Conservative substitutions to test the importance of specific properties

  • Radical substitutions to disrupt function

  • Reciprocal mutations between gorilla and human/chimpanzee orthologs

• Functional assessment protocols:

  • Compare EC50 values for identified agonists

  • Assess receptor surface expression with and without mutations

  • Measure activation kinetics and signal amplitude

• Structural modeling integration:

  • Use homology models to predict effects before testing

  • Update models based on functional results

  • Identify networks of residues acting cooperatively

• Evolutionary context analysis:

  • Focus on positions showing signatures of positive selection

  • Examine conservation patterns across primates

  • Consider variations specific to the gorilla lineage

This approach systematically maps the molecular determinants of agonist specificity and receptor function, providing insights into how evolutionary changes have shaped TAS2R13 function in gorillas compared to other primates .

What high-throughput approaches can accelerate the identification of gorilla TAS2R13 agonists?

Modern high-throughput methods for agonist discovery:

High-Throughput Screening Approaches:

• Cell-based fluorescence assays:

  • Automated calcium imaging in plate formats (96/384-well)

  • FLIPR-based screening with calcium-sensitive dyes

  • Real-time kinetic measurements to capture transient responses

• Receptor internalization assays:

  • Fluorescently tagged receptors to track endocytosis upon activation

  • Automated microscopy with image analysis algorithms

  • Correlation of internalization with functional activation

• Compound library design:

  • Focused libraries of plant compounds from gorilla food plants

  • Chemoinformatic approaches to select diverse bitter compounds

  • Natural extract libraries from plants in gorilla habitats

• Bioluminescence resonance energy transfer (BRET):

  • Measure receptor-G protein interactions directly

  • Lower false positive/negative rates than calcium assays

  • Allows detection of ligands with different efficacy profiles

• Computational pre-screening:

  • Virtual screening against homology models

  • Pharmacophore-based filtering of compound libraries

  • Machine learning to predict agonists based on known activators of related receptors

These approaches dramatically increase throughput compared to traditional methods, enabling comprehensive agonist profiling of gorilla TAS2R13 against hundreds or thousands of compounds in days rather than months .

What are the implications of gorilla TAS2R13 research for understanding sensory ecology across primates?

The broader implications of gorilla TAS2R13 research extend across multiple domains:

Gorilla TAS2R13 research provides a critical comparative perspective on sensory evolution in primates. By understanding how this receptor functions in gorillas compared to humans and other apes, researchers can reconstruct the evolutionary history of bitter taste perception and its relationship to dietary specialization. Evidence from related TAS2R genes indicates that these receptors are often narrowly tuned and show species-specific activation patterns, suggesting independent evolution of bitter taste sensitivities in different primate lineages . This research helps explain how closely related species can occupy different dietary niches through sensory adaptations, contributing to our understanding of primate diversification and adaptation to varied habitats.

The discovery of bitter taste receptors as targets of selection and potential adaptive introgression in gorillas (as seen with TAS2R14) suggests that TAS2R13 may have played a similar role in gorilla adaptation . This connects sensory perception directly to fitness and survival in wild populations, illustrating how molecular evolution at the receptor level translates to ecological adaptation. Future research combining field observations of gorilla feeding behavior with genetic and functional studies of TAS2R13 will further illuminate these connections.

What emerging technologies will advance gorilla TAS2R13 research in the next decade?

Emerging technologies poised to transform this research area:

Transformative Technologies:

• CRISPR-based approaches:

  • Generation of gorilla-specific mutations in human cell lines

  • Creation of taste receptor knockout/in models

  • Precise editing of regulatory regions affecting expression

• Single-cell sequencing:

  • Examination of TAS2R13 expression in individual taste cells

  • Mapping of cell-specific transcriptional networks

  • Identification of co-expressed receptors and signaling components

• Organoid models:

  • Development of taste bud organoids expressing gorilla TAS2R13

  • More physiologically relevant testing environments

  • Potential for patient-specific testing with different genetic backgrounds

• Cryo-EM and advanced structural biology:

  • Direct structural determination of TAS2R13

  • Visualization of ligand-receptor complexes

  • Dynamic structural changes during activation

• Field-deployable genomics:

  • On-site genetic analysis of wild gorilla populations

  • Real-time correlation of genotypes with observed feeding behaviors

  • Non-invasive sampling methods for broader population coverage

These technologies will enable unprecedented insights into the molecular mechanisms, expression patterns, and ecological relevance of TAS2R13 in gorillas, advancing our understanding of both receptor biology and primate evolution.

How can integrative approaches combining genomics, functional studies, and ecological research advance our understanding of gorilla TAS2R13?

Integrative research frameworks offer the most comprehensive insights:

Integrative Research Model:

• Genomic-functional integration:

  • Correlation of genetic variants with functional differences in receptor activation

  • Identification of regulatory elements affecting expression levels

  • Population genomics to map TAS2R13 variation across gorilla subspecies and habitats

• Ecological contextualization:

  • Catalog bitter compounds in gorilla food plants across habitats

  • Test these compounds on recombinant receptors

  • Correlate receptor genotypes with feeding preferences in wild populations

• Evolutionary modeling:

  • Reconstruct ancestral TAS2R13 sequences and test their function

  • Model selection pressures across primate lineages

  • Test for evidence of adaptive introgression using methods like S* and VolcanoFinder

• Physiological relevance:

  • Connect receptor activation thresholds to natural compound concentrations

  • Understand how receptor polymorphisms affect behavioral responses

  • Investigate potential health implications of TAS2R13 variation

• Conservation applications:

  • Use TAS2R13 as a marker for population diversity

  • Inform habitat management based on sensory adaptations

  • Consider sensory ecology in captive diet formulation