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Bitter taste receptors (TAS2Rs) are a poorly understood subgroup of G protein-coupled receptors (GPCRs). The experimental structure of these receptors has yet to be determined, and key-residues controlling their function remain mostly unknown. We designed an integrative approach to improve comparative modeling of TAS2Rs. Using current knowledge on class A GPCRs and existing experimental data in the literature as constraints, we pinpointed conserved motifs to entirely re-align the amino-acid sequences of TAS2Rs. We constructed accurate homology models of human TAS2Rs. As a test case, we examined the accuracy of the TAS2R16 model with site-directed mutagenesis and in vitro functional assays. This combination of in silico and in vitro results clarifies sequence-function relationships and proposes functional molecular switches that encode agonist sensing and downstream signaling mechanisms within mammalian TAS2Rs sequences. [ABSTRACT FROM AUTHOR]

Odorant receptors represent the largest family of mammalian G protein-coupled receptors. Phylogenetically, they are split into two classes (I and II). By analyzing the entire subclass I odorant receptors sequences, we identified two class I-specific and highly conserved motifs. These are predicted to face each other at the extra-cellular portion of the transmembrane domain, forming a vestibular site at the entrance to the orthosteric-binding cavity. Molecular dynamics simulation combined with site-directed mutagenesis and in vitro functional assays confirm the functional role of this vestibular site in ligand-driven activation. Mutations at this part of the receptor differentially affect the receptor response to four agonists. Since this vestibular site is involved in ligand recognition, it could serve ligand design that targets specifically this sub-genome of mammalian odorant receptors. [ABSTRACT FROM AUTHOR]