Sweet taste receptors are a topic of interest for culinary enthusiasts. In mammals, sweet taste is predominantly transduced through family 1 taste receptors: T1R2 and T1R3. These are G protein coupled-receptors which dimerise to form the sweet receptor complex (SRC), increasing their sensitivity to sweet tastants. Compounds have been developed that are sweeter and less calorific than their natural counterparts. While previous studies have suggested differences in their sweetness relative to sucrose, comprehensive examination of their activity at the canonical sweet receptors have not yet been completed.
The objective of this study was to characterise T1R receptors’ activity and interactions at the receptor/G protein level (expressed in HEK293 cells). Using BRET2 based biosensors for protein dissociation (Olsen et al., 2020), it was determined that T1Rs employ a variety of G proteins to transduce their signal. T1R stimulation by sweet compounds primarily induced inhibitory Gi/0 proteins over the stimulatory Gs proteins, which was corroborated by cAMP accumulation assays. Furthermore Gq/11 Ca2+ mobilising G proteins were also activated which was verified using the Fluo-4 photo activity assays. Additionally, G13 dissociation was observed, and this was consistent with transcriptional activity at the serum response factor response element (SRF-RE), which is downstream of RhoA activation. Greater dissociation of G proteins was observed when the T1Rs were combined as the SRC, and this promoted bias toward Ca2+ mobilising G proteins.
These results represent the first systematic analysis of G protein activation and signalling bias at the T1Rs. One example is the tendency for man-made sweeteners to bias toward Ca2+ mobilising G proteins (suggested to be responsible for taste transduction) compared to naturally derived ones. The study displays the basis for further research into these receptors at tissue level, where expressed G proteins may vary.
Research funded by AstraZeneca.