Functional molecular switches of mammalian G protein-coupled bitter-taste receptors

Abstract

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 aminoacid 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 clarify sequence-function relationships and identify the functional molecular switches that encode agonist sensing and downstream signaling mechanisms within mammalian TAS2Rs sequences.

Structural basis for strychnine activation of human bitter taste receptor TAS2R46

“…S11, A, C, and D). Together with previous modeling and bioinformatic works ( 23 , 30 , 33 , 50 ), these findings provide clues for the understanding of broad-spectrum ligand recognition of TAS2R46, which may help to identify or design other chemical entities for bitter taste receptors.…”

“…4D), which may aid ligand binding and receptor activation. Residue Y 6.48T in TAS2R46 is not highly conserved among TAS2Rs, implying that diverse activation mechanisms may exist in other bitter taste receptors or with other ligands ( 30 ).…”

“…In strychnine-bound TAS2R46, the corresponding residues are F 3.49 Y 3.50 L 3.51 , and this motif is relatively conserved in TAS2Rs (fig. S9I and movie S2) ( 30 ). Our results are consistent with the involvement of this region in G protein binding—Y106 3.50 forms a hydrogen bond with the carbonyl oxygen of residue C351 from the Gα gust α5 helix, and the mutation F105 3.49 A or Y106 3.50 A impairs the activation of TAS2R46 by strychnine (Fig.…”

“…The ligand recognition pattern of TAS2R46 was further explored through molecular docking studies. A list of 68 bitter molecules was retrieved from BitterDB ( 22 , 30 , 33 ) for molecular docking, and the representative binding poses were analyzed. In agreement with the strychnine-bound TAS2R46 structure and previous molecular simulation studies ( 32 ), W88 3.32 and E265 7.39 play the most critical roles in the recognition and coordination of these molecules.…”

“…Here, we report the cryo-electron microscopy (cryo-EM) structures of TAS2R46 in complex with chimeric mini-G protein gustducin, in a potent neurotoxin strychnine-bound form, and in the apo form. In combination with previous computational modeling and mutagenesis studies (22,(30)(31)(32), the structures reveal molecular features of class T GPCRs, which is the last structureless class of GPCRs, contributing to a deeper understanding of the biology behind bitter taste perception and signaling.…”