Characterization of the Modes of Binding between Human Sweet Taste Receptor and Low-Molecular-Weight Sweet Compounds

Ayako Koizumi,Takaharu Tanaka,Takumi Misaka,Keiko Abe,Wolfgang Meyerhof,Ken-ichiro Nakajima,Masaji Ishiguro,Katsuyoshi Masuda

doi:10.1371/journal.pone.0035380

Abstract

One of the most distinctive features of human sweet taste perception is its broad tuning to chemically diverse compounds ranging from low-molecular-weight sweeteners to sweet-tasting proteins. Many reports suggest that the human sweet taste receptor (hT1R2–hT1R3), a heteromeric complex composed of T1R2 and T1R3 subunits belonging to the class C G protein–coupled receptor family, has multiple binding sites for these sweeteners. However, it remains unclear how the same receptor recognizes such diverse structures. Here we aim to characterize the modes of binding between hT1R2–hT1R3 and low-molecular-weight sweet compounds by functional analysis of a series of site-directed mutants and by molecular modeling–based docking simulation at the binding pocket formed on the large extracellular amino-terminal domain (ATD) of hT1R2. We successfully determined the amino acid residues responsible for binding to sweeteners in the cleft of hT1R2 ATD. Our results suggest that individual ligands have sets of specific residues for binding in correspondence with the chemical structures and other residues responsible for interacting with multiple ligands.

Highlights

The human sweet taste receptor is a heteromeric complex composed of two subunits, T1R2 and T1R3, which are class C G protein–coupled receptors (GPCRs) [1,2,3]
Each subunit has a large amino-terminal domain (ATD) linked by an extracellular cysteine-rich domain (CRD) to a seventransmembrane helical domain (TMD) [4]. hT1R2–hT1R3 responds to a wide variety of chemical substances including naturally occurring sugars, D-amino acids (D-tryptophan and D-phenylalanine) and glycosides, as well as artificial chemical compounds such as sucralose, aspartame, neotame, saccharin Na, acesulfame K (AceK), and cyclamate (Fig. 1) [5]
Mutagenesis studies for screening the residues responsible for sweetener recognition To define the binding modes of sweeteners at the cleft formed by LB1 and LB2 of hT1R2 ATD, we carried out a series of mutagenesis studies on hT1R2 ATD

Summary

Introduction

The human sweet taste receptor (hT1R2–hT1R3) is a heteromeric complex composed of two subunits, T1R2 and T1R3, which are class C G protein–coupled receptors (GPCRs) [1,2,3]. Naturally occurring sweet proteins, such as brazzein, thaumatin, and monellin, and naturally occurring taste-modifying proteins, such as neoculin and miraculin, bind to hT1R2– hT1R3 [6,7,8,9,10,11]. The ATD of hT1R2 is responsible for binding to aspartame and sugar derivatives [9]. Neoculin binds the ATD of hT1R3 [12].

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Conclusion