Structural requirements of bitter taste receptor activation

Abstract

An important question in taste research is how 25 receptors of the human TAS2R family detect thousands of structurally diverse compounds. An answer to this question may arise from the observation that TAS2Rs in general are broadly tuned to interact with numerous substances. Ultimately, interaction with chemically diverse agonists requires architectures of binding pockets tailored to combine flexibility with selectivity. The present study determines the structure of hTAS2R binding pockets. We focused on a subfamily of closely related hTAS2Rs exhibiting pronounced amino acid sequence identities but unique agonist activation spectra. The generation of chimeric and mutant receptors followed by calcium imaging analyses identified receptor regions and amino acid residues critical for activation of hTAS2R46, -R43, and -R31. We found that the carboxyl-terminal regions of the investigated receptors are crucial for agonist selectivity. Intriguingly, exchanging two residues located in transmembrane domain seven between hTAS2R46, activated by strychnine, and hTAS2R31, activated by aristolochic acid, was sufficient to invert agonist selectivity. Further mutagenesis revealed additional positions involved in agonist interaction. The transfer of functionally relevant amino acids identified in hTAS2R46 to the corresponding positions of hTAS2R43 and -R31 resulted in pharmacological properties indistinguishable from the parental hTAS2R46. In silico modeling of hTAS2R46 allowed us to visualize the putative mode of interaction between agonists and hTAS2Rs. Detailed structure-function analyses of hTAS2Rs may ultimately pave the way for the development of specific antagonists urgently needed for more sophisticated analyses of human bitter taste perception.calcium imaging | G protein-coupled receptors | hTAS2R

Amino Acid Derivatives as Bitter Taste Receptor (T2R) Blockers

“…Similarly, with T2R46 the ECL2 mutant N150K displayed reduced agonist binding (14). In most of the T2Rs, TM3 plays a crucial role in ligand binding (13,15,(32)(33)(34)(35). In the first part of this structure-function study, the quinine-binding pocket of the moderately tuned T2R4 was elucidated.…”

“…T2Rs are one of the least studied and understood GPCR subfamilies. Structure-function studies to understand ligand binding have been carried out on 9 of the 25 T2Rs, including T2R1 (10), T2R10 (11), T2R14 (12), T2R16 (13), T2R30 (14), T2R38, T2R43, T2R44 (T2R31), and T2R46 (15). In T2Rs, the extracellular residues on transmembrane (TM) helices TM3, TM6, and TM7 are predominantly involved in ligand binding.…”

Comprehensive Analysis of Mouse Bitter Taste Receptors Reveals Different Molecular Receptive Ranges for Orthologous Receptors in Mice and Humans

“…A neighbor-joining tree (ClustalX (122)) was constructed after manual adjustment while considering previous in silico and in vitro experiments (29,30). Bootstrap values computed using 10,000 iterations were subsequently inferred.…”

“…24 -28). However, structure-function analyses of human bitter taste receptors reveal that very few differences in the amino acid sequences of TAS2R can account for the largely deviating agonist spectra (29). Conversely, human TAS2R paralogs with pronounced amino acid sequence differences can have agonists in common even though they recognize these compounds by different binding modes (30).…”

Knowledge Based Membrane Protein Structure Prediction: From X-Ray Crystallography to Bioinformatics and Back to Molecular Biology

“…on hTAS2R16 and hTAS2R38 relied on computations only (Floriano et al, 2006;Miguet et al, 2006). In addition, three experimentally guided structure-activity studies are available now, which all addressed hTAS2Rs distantly related to hTAS2R38 (Brockhoff et al, 2010;Pronin et al, 2004;Sakurai et al, 2010). First principle (Floriano et al, 2006) and homology modeling approaches based on bovine rhodopsin (Miguet et al, 2006) have been used to predict the structure of the widely studied bitter taste receptor hTAS2R38 (Bufe et al, 2005;Khafizov et al, 2007;Kim et al, 2003;Kleinau et al, 2007).…”