Figure 2

Effect of lactisole on Tas1r3 variants. (a) Calcium responses of cells co-transfected with hTAS1R2 and a Tas1r3 chimera comprising the human N-terminus and the rat transmembrane region or hTAS1R2 and a Tas1r3 chimera comprising the rat N-terminus and the human transmembrane region (b) to stimulation with various sweeteners in the presence and absence of lactisole. c, response of mock-transfected control cells; lac, 1.0 mM lactisole; asp, 15 mM aspartame; cyc, 30 mM cyclamate; neo, 0.1 mM neohesperidine dihydrochalcone; sac, 10 mM saccharin; suc, 100 mM sucrose; stev, 1 mM stevioside; -, response without lactisole; +, response in the presence of 1.0 mM lactisole. All sweeteners were used at concentrations which were close to the maximal obtainable signal. (c) Alignment of amino acid sequences of the human, rat, and mouse Tas1r3 transmembrane regions. Color code: white, identical; grey, conservative; dark-grey, similar; black, non-similar. TM, predicted transmembrane domain, indicated by a black bar. Dots indicate the location of the primer used to generate the chimeric rat-human Tas1r3 receptors. Asterisks denote amino acid positions that are identical in rat and mouse but variable between humans and rodents and are located in the extracellular loops or the upper part of the transmembran regions. Boxes indicate the several rTas1r3 mutants m1 – m7, including the amino acid substitutions. m6/1 – m6/3 signified the reconverted amino acid of mutant m6.