Brazzein and monellin are two naturally occurring plant proteins perceived as sweet by humans, which share no sequence or structural similarity. Both of these proteins like all classes of sweet compounds are perceived through the activation of the T1R2/T1R3 heterodimeric sweet taste receptor. T1R2 and T1R3 subunits are members of the small family of class C G-protein coupled receptors (GPCRs). Class C GPCRs possess a large N-terminal domain (NTD) linked to a heptahelical transmembrane domain by a cysteine rich domain (CRD). The NTD of T1R2 (T1R2-NTD) has been shown to contain the primary binding site for most of the sweet ligands including natural sugars, D-amino acids, and artificial sweeteners. While residues in hT1R2-NTD have been shown to be required for the receptor response to monellin, site-directed mutagenesis have demonstrated that CRD of human T1R3 is determinant for receptor activation to brazzein. In contrast, molecular modeling and docking studies have proposed a hypothetical ‘wedge model’ in which both of these sweet proteins may interact in a multi-point binding mode to an external site of the sweet receptor NTDs. To elucidate the individual contribution of both receptor subunits to brazzein and monellin detection, we recombinantly expressed human T1R2- and T1R3-NTDs in Escherichia coli. T1R2 and T1R3-NTD were tested separately for their ability to interact with sugar and sweeteners using intrinsinc fluorescence. We then measured the interactions of T1R2 and T1R3-NTDs with the two recombinant sweet-tasting proteins, using Bio-Layer Interferometry (BLI). This optical technique analyzes the signal variations in the interference pattern generated from visible light reflected from an optical layer and a biolayer containing the immobilized protein of interest. This recent method is powerful for studying protein-protein interactions and measuring both affinity constants and kinetic parameters. BLI experiments demonstrated that T1R2-NTD binds brazzein and monellin with Kd values in the physiological range. These affinities are in agreement with the capacity of these sweet-tasting proteins to activate T1R2/T1R3 receptor heterologously expressed in HEK cells and with sensory experiments conducted on humans. We will discuss these data in regards to the wedge model, which will be further investigated using site-directed mutagenesis.