Valine 738 and lysine 735 in the fifth transmembrane domain of rTas1r3 mediate insensitivity towards lactisole of the rat sweet taste receptor

BACKGROUND: The sweet taste inhibitor lactisole acts on the human sweet taste receptor heteromer TAS1R2-TAS1R3 but not on its rodent counterpart. Recently, it was shown that the lactisole sensitivity of the human sweet taste receptor involves the part of TAS1R3 encompassing the seven transmembrane regions but not the huge N-terminal domain. Using mutational analysis we investigated which amino acid residues distinguish lactisole insensitive rat from sensitive human T1R3 receptors. RESULTS: The functional analysis of specific receptor mutants in HEK293T cells revealed that the exchange of valine 738 in the fifth transmembrane domain of rTas1r3 by an alanine is sufficient to confer lactisole sensitivity to the rat sweet taste receptor. The sensitivity of this receptor mutant is ~2 fold lower than the sensitivity of the human sweet taste receptor. Additional substitution of lysine 735 by phenylalanine in rTas1r3 results in a rat sweet taste receptor that is as sensitive to lactisole as its human counterpart. The exchange of valine 738 to alanine was accompanied by a ~50% reduction in receptor efficacy. This effect was seen with all six different sweet compounds examined. CONCLUSION: The lactisole insensitivity of rat sweet taste receptor is caused by only two amino acids in transmembrane region five, which is critical for the interaction of lactisole with the sweet taste receptor. The observation that the mutant receptor simultaneously displays a generally reduced sensitivity towards all agonists suggests that the lactisole insensitivity of the rodent receptor might be more likely caused by the inaccessibility of the lactisole binding site rather then by its direct disruption

Bacterial MgrB peptide activates chemoreceptor Fpr3 in mouse accessory olfactory system and drives avoidance behaviour

Innate immune chemoreceptors of the formyl peptide receptor (Fpr) family are expressed by vomeronasal sensory neurons (VSNs) in the accessory olfactory system. Their biological function and coding mechanisms remain unknown. We show that mouse Fpr3 (Fpr-rs1) recognizes the core peptide motif f-MKKFRW that is predominantly present in the signal sequence of the bacterial protein MgrB, a highly conserved regulator of virulence and antibiotic resistance in Enterobacteriaceae. MgrB peptide can be produced and secreted by bacteria, and is selectively recognized by a subset of VSNs. Exposure to the peptide also stimulates VSNs in freely behaving mice and drives innate avoidance. Our data shows that Fpr3 is required for neuronal detection and avoidance of peptides derived from a conserved master virulence regulator of enteric bacteria

The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor-2

<p><b>Copyright information:</b></p><p>Taken from "The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor"</p><p>http://www.biomedcentral.com/1472-6807/7/66</p><p>BMC Structural Biology 2007;7():66-66.</p><p>Published online 12 Oct 2007</p><p>PMCID:PMC2099433.</p><p></p>and extra cellular loops are removed and the helices are directly connected. The transmembrane segments (TM1–TM7) are denoted in orange. Important residues are labeled in Ballesteros-Weinstein nomenclature in addition to the one letter amino acid code. Amino acids that influence the activation of the sweet receptor by NHDC are shown as spheres. The size of the spheres corresponds to the size of the side chain. The spheres are colored according to their pharmacophoric properties. Hydrophobic amino acids (F, P, M, A, L, I, G, V, W) cyan, H-donor/acceptor (Y, T, S, H, C, N, Q) magenta, H-bond donors with a positive charge (R) blue. Possible H-bond interactions are presented as dotted lines The color of the dotted lines indicate the energy of a H-bond, blue indicates an energy of -0.3–0.6 kcal/Mol, magenta: -0.6–1.2 kcal/Mol, red: -1.2–2.4 kcal/Mol. C atoms of NHDC are displayed in white and oxygen in red. Amino acid positions printed in red refer to residues emerged from the first round of mutational analysis and have been used as anchor points. Amino acid positions printed in grey were predicted from the model to influence receptor activation by NHDC and have been verified by mutational analysis

The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor-4

<p><b>Copyright information:</b></p><p>Taken from "The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor"</p><p>http://www.biomedcentral.com/1472-6807/7/66</p><p>BMC Structural Biology 2007;7():66-66.</p><p>Published online 12 Oct 2007</p><p>PMCID:PMC2099433.</p><p></p> (B) Representative calcium traces elicited upon stimulation with different concentrations of neohesperidin dihydrochalcone (NHDC) in HEK293T-G16Gust44 cells cotransfected with DNA for hTAS1R2/hTAS1R3. (C,D) Calcium responses of cells cotransfected with DNA for different rat and human subunits or chimeras upon stimulation with 1 mM NHDC (C), or 30 mM D-Tryptophan (D). R, rat receptor subunit; H human receptor subunit; HR, receptor chimera comprising the N-terminal extra cellular domain of the human receptor subunit fused to the corresponding heptahelical domain of the rat; RH, comprising the N-terminal extracellular domain of the rat receptor subunit fused to the corresponding heptahelical domain of the human receptor

The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor-0

<p><b>Copyright information:</b></p><p>Taken from "The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor"</p><p>http://www.biomedcentral.com/1472-6807/7/66</p><p>BMC Structural Biology 2007;7():66-66.</p><p>Published online 12 Oct 2007</p><p>PMCID:PMC2099433.</p><p></p>ked by ICL and ECL, respectively. Amino acids that influence allosteric modulator activity in hCaSR, hmGlu2, rmGlu1 and 5 are marked in grey. Positions that alter the response of the sweet receptor to lactisole, cyclamate, or NHDC are shown in red. Asterisks indicate residues involved in receptor activation by NHDC (orange) or cyclamate (blue). Green asteriks denote residues mediating sensitivity of the receptor to lactisole

The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor-1

<p><b>Copyright information:</b></p><p>Taken from "The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor"</p><p>http://www.biomedcentral.com/1472-6807/7/66</p><p>BMC Structural Biology 2007;7():66-66.</p><p>Published online 12 Oct 2007</p><p>PMCID:PMC2099433.</p><p></p> different lactisole concentrations. No lactisole present (filled circles, solid line), 50 μM lactisole (filled triangles up, dashed line), and 100 μM lactisole (filled squares, dash-dotted line). (E) ECvalues for acesulfame K, aspartame, NHDC, and cyclamate in the absence or presence of 50 μM and 100 μM lactisole

The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor-3

<p><b>Copyright information:</b></p><p>Taken from "The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor"</p><p>http://www.biomedcentral.com/1472-6807/7/66</p><p>BMC Structural Biology 2007;7():66-66.</p><p>Published online 12 Oct 2007</p><p>PMCID:PMC2099433.</p><p></p>tisole in HEK293T-G16Gust44 cells cotransfected with DNA for wild type hTAS1R2/hTAS1R3 (filled circle, solid line), C801I(open diamond, short dashed line), Y699L(open circle, dash-dot-dotted line), Y699F(filled triangle up, medium dashed line), or W775A(filled hexagon, dash-dotted line) and hTAS1R2 DNA. (B) Concentration-dependent responses of HEK293T-G16Gust44 cells to cyclamate cotransfected with DNA for hTAS1R3 (filled circle, solid line), S726A(open triangle up, medium dashed line), C801I(open diamond, short dashed line), or W775A(filled hexagon, dash-dotted line) and hTAS1R2

The Molecular Basis of Individual Differences in Phenylthiocarbamide and Propylthiouracil Bitterness Perception

AbstractIndividual differences in perception are ubiquitous within the chemical senses: taste, smell, and chemical somesthesis [1–4]. A hypothesis of this fact states that polymorphisms in human sensory receptor genes could alter perception by coding for functionally distinct receptor types [1, 5–8]. We have previously reported evidence that sequence variants in a presumptive bitter receptor gene (hTAS2R38) correlate with differences in bitterness recognition of phenylthiocarbamide (PTC) [9–11]. Here, we map individual psychogenomic pathways for bitter taste by testing people with a variety of psychophysical tasks and linking their individual perceptions of the compounds PTC and propylthiouracil (PROP) to the in vitro responses of their TAS2R38 receptor variants. Functional expression studies demonstrate that five different haplotypes from the hTAS2R38 gene code for operatively distinct receptors. The responses of the three haplotypes we also tested in vivo correlate strongly with individuals' psychophysical bitter sensitivities to a family of compounds. These data provide a direct molecular link between heritable variability in bitter taste perception to functional variations of a single G protein coupled receptor that responds to compounds such as PTC and PROP that contain the N-C=S moiety. The molecular mechanisms of perceived bitterness variability have therapeutic implications, such as helping patients to consume beneficial bitter-tasting compounds—for example, pharmaceuticals and selected phytochemicals