Five amino acid residues in cysteine-rich domain of human T1R3 were involved in the response for sweet-tasting protein, thaumatin

Abstract

Thaumatin, a sweet-tasting plant protein, elicits a sweet taste sensation at 50 nM in humans but not rodents. Although it was shown that the cysteine-rich domain (CRD) of human T1R3 (hT1R3) is important for the response to thaumatin, the amino acid residues within CRD critical for response are still unknown. A comparison of the amino acid sequence (69 amino acid residues) of CRD between hT1R3 and mouse T1R3 (mT1R3) revealed sixteen amino acids that differ. In the present study, we converted each of these sixteen amino acids in hT1R3 to their mouse counterpart and examined the response to thaumatin and sucralose using a cell-based assay. No significant decrease in the response to sucralose was seen among any of the sixteen mutants. However, five mutants (Q504K, A537T, R556P, S559P, and R560K) exhibited a significantly diminished response to thaumatin. The five critical residues involved in the response to thaumatin were dispersed in the CRD of hT1R3 and widely distributed when compared to brazzein. The unique intense sweet-taste of thaumatin might be attributed to the different receptor activation mechanism compared to the small molecule sweetener sucralose.

Aspergillus fumigatus CalA binds to integrin α5β1 and mediates host cell invasion

“…This diverse group of proteins is present in some Ascomycete and Basidiomycete fungi, as well as in plants, nematodes, and insects 27,28 . Some thaumatin-like proteins have a sweet taste because they bind to G protein-coupled receptors in the taste buds 29 . The data presented herein indicate that A. fumigatus CalA functions as an invasin by binding to a different host receptor, integrin α5β1, thereby inducing host cell endocytosis of adherent organisms.…”

Sweet Taste-Sensing Receptors Expressed in Pancreatic β-Cells: Sweet Molecules Act as Biased Agonists

“…In addition, cyclamate and lactisole, an inhibitor of human T1R3, bind to the transmembrane domain of T1R3 [24], which may also function as an allosteric binding site for saccharin [25]. There is a possibility that the cysteine-rich domain offers another binding domain for protein sweeteners [26,27]. …”

Effect of Transgenesis on mRNA and miRNA Profiles in Cucumber Fruits Expressing Thaumatin II

“…Insertion of the transgene expression cassette into the cucumber genome was confirmed by PCR amplification using primers designed to amplify the thaumatin II and nptII (kanamycin resistance) gene fragments. Two pairs of primers designed to amplify the thaumatin II gene fragment were used: Tha_S_F 5 -TCCTCCTCCTCACGCTCTCC-3 and Tha_S_R 5 -AGCCAATCCCCACACACATA-3 [12]; and Tha_M_F 5 -GCCACCTTCGAGATCGTCAAC-3 and Tha_M_R 5 -TGTCGTCGAAATAGC AGTCG-3 [24]. Primers nptII_F 5 -GAGGCTATTCGGCTATGAACTG-3 and nptII_R 5 -ATCGGGA GCGGCGATACCGTA-3 were used to amplify the nptII gene fragment.…”