Dubovski Nitzan, Ben-Shoshan Galeczki Yaron, Malach Einav, Niv Masha Y
The Institute of Biochemistry, Food Science and Nutrition, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel.
Chem Senses. 2023 Jan 1;48. doi: 10.1093/chemse/bjad005.
We have previously shown that l-glucose, the non-caloric enantiomer of d-glucose, activates the human sweet taste receptor T1R2/T1R3 transiently expressed in HEK293T cells. Here, we show that d- and l-glucose can also activate T1R2 and T1R3 expressed without the counterpart monomer. Serine mutation to alanine in residue 147 in the binding site of T1R3 VFT domain, completely abolishes T1R3S147A activation by either l- or d-glucose, while T1R2/T1R3S147A responds in the same way as T1R2 expressed without its counterpart. We further show that the original T1R2 reference sequence (NM_152232.1) is less sensitive by almost an order of magnitude than the reference sequence at the time this study was performed (NM_152232.4). We find that out of the four differing positions, it is the R317G in the VFT domain of T1R2, that is responsible for this effect in vitro. It is significant for both practical assay sensitivity and because glycine is found in this position in ~20% of the world population. While the effects of the mutations and the partial transfections were similar for d and l enantiomers, their dose-response curves remained distinct, with l-glucose reaching an early plateau.
我们之前已经表明，l-葡萄糖，即d-葡萄糖的无热量对映体，能够激活在HEK293T细胞中瞬时表达的人类甜味受体T1R2/T1R3。在此，我们表明d-葡萄糖和l-葡萄糖也能够激活在没有对应单体的情况下表达的T1R2和T1R3。T1R3 VFT结构域结合位点中第147位残基的丝氨酸突变为丙氨酸，完全消除了l-葡萄糖或d-葡萄糖对T1R3S147A的激活作用，而T1R2/T1R3S147A的反应方式与没有对应单体时表达的T1R2相同。我们进一步表明，原始的T1R2参考序列（NM_152232.1）的敏感性比本研究进行时的参考序列（NM_152232.4）低近一个数量级。我们发现，在四个不同的位置中，是T1R2的VFT结构域中的R317G导致了这种体外效应。这对于实际检测灵敏度都很重要，并且因为在世界约20%的人口中该位置存在甘氨酸。虽然d-对映体和l-对映体的突变和部分转染的效应相似，但它们的剂量反应曲线仍然不同，l-葡萄糖达到早期平台期。
