Sweet Taste Receptors
The sweet taste receptor is a heterodimer of TAS1R2 and TAS1R3 (Type 1 taste receptors 2 and 3), two GPCRs with large Venus flytrap extracellular domains. It detects sugars, sugar alcohols, artificial sweeteners (aspartame, saccharin, sucralose), and sweet proteins (thaumatin, brazzein, miraculin). Each class binds at a different site on the dimer, contributing to the receptor's broad spectrum of sweet ligand recognition.
Binding Diversity
Sugars and amino acid derivatives (aspartame) bind primarily in TAS1R2's Venus flytrap. Saccharin and cyclamate bind at the TAS1R3 transmembrane domain. Brazzein binds the TAS1R3 cysteine-rich domain. This structural diversity explains why different sweet compounds taste subtly different — each activates the receptor through a different conformational pathway, producing slightly different downstream signal kinetics.
Engineering Sweetness
The IFI-S axis scores TAS1R2/TAS1R3 activation relative to sucrose at receptor saturation. Engineering targets include overexpressing thaumatin (sweet protein, ~2000× sucrose potency by mass) in target crops, increasing trehalose content through trehalose-6-phosphate synthase overexpression, or introducing miraculin (the taste-modifying sweet protein from miracle fruit) as a sweetness amplifier that works specifically at acidic pH.