Systematic analysis reveals novel insight into the molecular determinants of function, diversity and evolution of sweet taste receptors T1R2/T1R3 in primates

Abstract

Sweet taste is a primary sensation for the preference and adaption of primates to diet, which is crucial for their survival and fitness. It is clear now that the sweet perception is mediated by a G protein-coupled receptor (GPCR)-sweet taste receptor T1R2/T1R3, and many behavioral or physiological experiments have described the diverse sweet taste sensitivities in primates. However, the structure-function relationship of T1R2s/T1R3s in primates, especially the molecular basis for their species-dependent sweet taste, has not been well understood until now. In this study, we performed a comprehensive sequence, structural and functional analysis of sweet taste receptors in primates to elucidate the molecular determinants mediating their species-dependent sweet taste recognition. Our results reveal distinct taxonomic distribution and significant characteristics (interaction, coevolution and epistasis) of specific key function-related residues, which could partly account for the previously reported behavioral results of taste perception in primates. Moreover, the prosimians Lemuriformes species, which were reported to have no sensitivity to aspartame, could be proposed to be aspartame tasters based on the present analysis. Collectively, our study provides new insights and promotes a better understanding for the diversity, function and evolution of sweet taste receptors in primates.

Keywords: coevolution; epistasis; molecular determinants; primate; species-dependent sweet taste; sweet taste receptor; taxonomic distribution.

FIGURE 1

Molecular simulations and schematic representation of the human sweet taste receptor. (A) Modeling of the human T1R2/T1R3 and its binding sites for different sweeteners. The conserved VFTM, CRD and TMD/ID region are colored in red, green and blue, respectively. The key residues involved in the species-dependent sweeteners (thaumatin and brazzein) recognition are labeled and shown as stick model. Residues appeared in other primates that mediate species-dependent sweet taste are colored in blue. (B) Binding site of aspartame in the sweet taste receptor. The receptor residues are shown in stick model and the water molecule is shown as red circle. Hydrogen bonds are shown as yellow solid lines. (C) Binding site of cyclamate in the sweet taste receptor. The residues in the pocket involved in cyclamate binding are according to the previous result (Jiang et al., 2005b). The figures were generated with the PyMOL software.

FIGURE 2

The phylogenetic tree analysis of sweet taste receptor T1R2 in primates. The percentages of replicate trees in which the associated taxa clustered together in the bootstrap test (1,000 replicates) are shown next to the branches, with branch lengths indicating the number of substitutions per site. The phyla and taxonomy of analyzed species are shown on the right.

FIGURE 3

The phylogenetic tree analysis of sweet taste receptor T1R3 in primates. The percentages of replicate trees in which the associated taxa clustered together in the bootstrap test (1,000 replicates) are shown next to the branches, with branch lengths indicating the number of substitutions per site. The phyla and taxonomy of analyzed species are shown on the right.

FIGURE 4

The protein sequence similarity networks (SSNs) of T1R2s and T1R3s in primates. (A) Protein sequences of T1R2s were analyzed to generate the network with an e-value threshold 10–5 (>96% sequence identity). The three nodes denoting T1R2 sequences of blue monkey and sykes’ monkey, rhesus macaque and stump-tailed macaque, and assam macaque and crab-eating macaque are overlapped respectively due to their same sequences. (B) Protein sequences of T1R3s were analyzed to generate the network with an e-value threshold 10–5 (>98% sequence identity). The three nodes denoting T1R3 sequences of blue monkey and sykes’ monkey, crab-eating macaque and stump-tailed macaque, and golden-bellied mangabey and sooty mangabey are overlapped respectively due to their same sequences. Each node represents one protein. Nodes from the same family in the networks are shown with the same color, and the colors corresponding to different families are listed on the right.

FIGURE 5

Multiple sequence alignment of T1R2s in primates. (A) Sequence logo representation of the conservation region and key residues mediating the sweet taste toward aspartame. The conservation level of each residue is indicated by the height of the bar above it. Residues involved in the sweet taste toward aspartame are underlined, and the two critical residues responsible for the species-dependent sweet taste toward aspartame are colored in red. This figuer was generated with the WebLogo 3 (https://weblogo.threeplusone.com/). (B) Sequence alignment of the two critical residues responsible for the species-dependent sweet taste toward aspartame. The proposed aspartame tasters are colored in light red while aspartame non-tasters are colored in blue.

FIGURE 6

Multiple sequence alignment of T1R3s in primates. (A) Sequence logo representation of the conservation region and key residues mediating the sweet taste toward brazzein, thaumatin and cyclamate. The conservation level of each residue is indicated by the height of the bar above it. The two critical residues responsible for the species-dependent sweet taste toward brazzein are colored in green. This figuer was generated with the WebLogo 3 (https://weblogo.threeplusone.com/). (B) Sequence alignment of the two critical residues responsible for the species-dependent sweet taste toward brazzein. The proposed brazzein tasters are colored in light red while brazzein non-tasters are colored in blue.