Biology subjects

Yasui, N.

Publications and source records attributed to Yasui, N..

3 recordsLinked to original sources

bioRxiv2025

Structural basis of stereochemical promiscuity by an umami taste receptor ortholog, Tas1r1/Tas1r3 from pufferfish

Taste receptor type 1 (TAS1R), which consists of sweet and umami receptors in humans, senses nutrients (such as sugars and amino acids) with substrate specificity that is often broad and varies among animals and subtypes. However, the structural basis for achieving diverse specificities remains largely elusive. Here, we present the crystal structure of the ligand-binding domain (LBD) of Tas1r1/Tas1r3 heterodimer from pufferfish, an ortholog of the human umami taste receptor. The overall structure of Tas1r1/Tas1r3LBD resembles previously reported TAS1R structures, indicating a conserved core architecture within the family. Nevertheless, pufferfish Tas1r1/Tas1r3 was found to bind and respond to both L- and D-amino acids, even though TAS1Rs are considered to respond to either enantiomer. Structural and mutational analyses revealed that this non-rigorous stereochemical recognition is attributed to inter- subdomain interactions that latch the cleft containing the amino acid-binding site. These interactions prevent the cleft from fully opening, thereby stabilizing the active conformation, even if the ligand shares a different chirality. These results suggest that different substrate specificities in TAS1Rs can be acquired not only by the gain or loss of direct interactions with the substrate but also by the gain of intramolecular interactions, which alter the conformational equilibrium of the receptor.

biochemistry↗

bioRxiv2022

Chloride ion evokes taste sensation by binding to the extracellular ligand-binding domain of sweet/umami taste receptors

Salt taste sensation is multifaceted: NaCl at low or high concentrations is preferably or aversively perceived through distinct pathways. Cl- is thought to participate in taste sensation through an unknown mechanism. Here we describe Cl- ion binding and the response of taste receptor type 1 (T1r), a receptor family composing sweet/umami receptors. The T1r2a/T1r3 heterodimer from the medaka fish, currently the sole T1r amenable to structural analyses, exhibited a specific Cl- binding in the vicinity of the amino-acid-binding site in the ligand-binding domain (LBD) of T1r3, which is likely conserved across species, including human T1r3. The Cl- binding induced a conformational change in T1r2a/T1r3LBD at sub-to low-mM concentrations similar to canonical taste substances. Furthermore, oral Cl- application to mice increased impulse frequencies of taste nerves connected to T1r-expressing taste cells and promoted their behavioral preferences attenuated by a T1r-specific blocker or T1r3 knock-out. These results suggest that the Cl- evokes taste sensations by binding to T1r, thereby serving as another preferred salt taste pathway at a low concentration.

biophysics↗

bioRxiv2019

Differential scanning fluorimetric analysis of the amino-acid binding to taste receptor using a model receptor protein, the ligand-binding domain of fish T1r2a/T1r3

Taste receptor type 1 (T1r) is responsible for the perception of essential nutrients, such as sugars and amino acids, and evoking sweet and umami (savory) taste sensations. T1r receptors recognize many of the taste substances at their extracellular ligand-binding domains (LBDs). In order to detect a wide array of taste substances in the environment, T1r receptors often possess broad ligand specificities. However, the entire ranges of chemical spaces and their binding characteristics to any T1rLBDs have not been extensively analyzed. In this study, we exploited the differential scanning fluorimetry (DSF) to medaka T1r2a/T1r3LBD, a current sole T1rLBD heterodimer amenable for recombinant preparation, and analyzed their thermal stabilization by adding various amino acids. The assay showed that the agonist amino acids induced thermal stabilization and shifted the melting temperatures (Tm) of the protein. An agreement between the DSF results and the previous biophysical assay was observed, suggesting that DSF can detect ligand binding at the orthosteric-binding site in T1r2a/T1r3LBD. The assay further demonstrated that most of the tested L-amino acids, but no D-amino acid, induced Tm shifts of T1r2a/T1r3LBD, indicating the broad L-amino acid specificities of the proteins probably with several different manners of recognition. The Tm shifts by each amino acid also showed a fair correlation with the responses exhibited by the full-length receptor, verifying the broad amino-acid binding profiles at the orthosteric site in LBD observed by DSF.

biochemistry↗