Amino Acids and Peptides Activate at Least Five Members of the Human Bitter Taste Receptor Family

Amino acids and peptides represent important flavor molecules eliciting various taste sensations. Here, we present a comprehensive assessment of the interaction of various peptides and all proteinogenic amino acids with the 25 human TAS2Rs expressed in cell lines. L-Phenylalanine and L-tryptophan activate TAS2R1 and TAS2R4, respectively, whereas TAS2R4 and TAS2R39 responded to D-tryptophan. Structure-function analysis uncovered the basis for the lack of stereoselectivity of TAS2R4. The same three TAS2Rs or subsets thereof were also sensitive to various dipeptides containing L-tryptophan, L-phenylalanine, or L-leucine and to Trp-Trp-Trp, whereas Leu-Leu-Leu specifically activated TAS2R4. Trp-Trp-Trp also activated TAS2R46 and TAS2R14. Two key bitter peptides from Gouda cheese, namely, Tyr-Pro-Phe-Pro-Gly-Pro-Ile-His-Asn-Ser and Leu-Val-Tyr-Pro-Phe-Pro-Gly-Pro-Ile-His-Asn, both activated TAS2R1 and TAS2R39. Thus, the data demonstrate that the bitterness of amino acids and peptides is not mediated by specifically tuned TAS2Rs but rather is brought about by an unexpectedly complex pattern of sensitive TAS2Rs.