Table 1.

Summary of mutagenesis data

hT1R2Activities
SucraloseSucroseSE-2SE-3SteviosideSWT819
WT++++++
S40A+++
Y103A+++
D142A+++
P277A+/−+/−+++/−+
D278A++++
E302A+++
R383A+++
K65A+/−++
L279A++++
D307A+/−+
  • Among the 23 T1R2 residues tested in the mutagenesis analysis, the 10 residues that are crucial for sucrose/sucralose and/or SE-2/SE-3 activities are listed. Wild-type and mutant T1Rs were each cotransfected with T1R3 and assayed by using either FLIPR or calcium imaging. Sucralose was used at 2.5 mM, sucrose at 100 mM, SE-2 at 25 μM in the presence of sucralose, and SE-3 at 200 μM in the presence of sucrose. Stevioside (0.6 mM) responses were determined to support the molecular model. SWT819 (25 μM) was used as a control for protein expression. The three residues required for enhancer activities are in the lowest three rows. +, comparable activity with the wild-type (WT) receptor; −, no detectable activity; +/−, reproducible activity significantly below that of wild-type receptor (see Figs. S1 and S2 for details).