Seminar by Dr. Antonella Di Pizio

Leibniz-Institute for Food Systems Biology at the Technical University of Munich (Germany)

From chemistry to biology and back: molecular recognition of bitter molecules

Ligand-protein interactions are the basis of all biological processes in our body, including bitter taste perception. Bitter molecules are recognized by a repertoire of 25 TAS2R receptors, classified as Class A G protein-coupled receptors (GPCRs) for their 3D architecture and binding site location. However, TAS2Rs similarity to Class A GPCRs is very low (13-29% for the TM domains) and TAS2Rs harbor variations on the typical Class A sequence motifs, including the absence of the ECL2-TM3 disulphide bridge and the TM3 D[E]RY [1]. Despite low similarity structural templates, the combination of in-silico and in-vitro techniques allowed for the rationalization of ligand-receptor interactions and identification of novel agonists [2].

TAS2R14 is one of the most broadly tuned bitter taste receptors and is activated by chemically diverse natural and synthetic compounds. In the seminar, I will show our results on the molecular recognition process of this receptor. Using bioinformatics and chemoinformatics approaches, we have analysed the receptor binding site and identified the molecular features that determine the broad-tuning [3]. To investigate how the architecture and composition of the TAS2R14 binding pocket enables specific interactions with a complex array of chemically diverse bitter agonists, we have analysed the binding mode of seven different TAS2R14 agonists. 40 point-mutated receptor constructs were generated to investigate the contribution of 19 positions located in the receptor's binding pocket to activation by 7, demonstrating that TAS2R14 receptor provides a large number of agonist-selective contact points, allowing for the recognition of chemical diverse compounds through different binding modes [4].

Flufenamic acid, the most potent and selective agonist for TAS2R14, was then used as lead structure for the design and synthesis of 19 derivatives. This work led to the identification of new TAS2R14 agonists with improved potency compared to flufenamic acid. Interestingly, a novel bis-trifluoromethyl-substituted tetrazole-derivative displayed not only high potency but also a substantial ceiling effect in three different functional assays, indicating partial agonist/partial antagonist properties (unpublished data). Even though TAS2R14 is a broadly-tuned receptor capable of accommodating compounds diverse in size and molecular properties, we showed that slight modifications in the flufenamic acid structure may drastically decrease and abolish TAS2R14 activity or shift the agonism towards antagonism.

BIBLIOGRAPHY

1.    Di Pizio, Levit, Slutzki, et al. Methods in cell biology 132, 401-427

2.    Di Pizio, Kruetzfeldt, Cheled-Shoval, et al. Scientific Reports 7 (1), 8223

3.    Di Pizio and Niv. Bioorganic & medicinal chemistry 23 (14), 4082-4091

4.    Nowak, Di Pizio, Levit, et al. BBA-General Subjects 1862 (10), 2162-2173