Periodic Reporting for period 2 - AlloGPCR (Allosteric modulation of G-protein Coupled Receptors conformational landscape)
Reporting period: 2020-09-01 to 2021-08-31
By reconstituting the GHSR in lipid discs with various lipid composition we confirmed the role of lipids as allosteric GPCR modulators. We then used the GHSR to study the conformational rearrangements of the receptor using fluorescence spectroscopy. We investigated the importance of water molecules and the hydration state of the receptor during the activation process. Our findings, backed by molecular dynamic (MD) simulations, suggest a role for the hydration network of the receptor during activation. In particular, we reported changes in the hydration patterns at specific receptor regions that are known to undergo conformational changes during receptor activation. Interestingly, the changes observed were different in the case of bias agonists, suggesting distinct conformations of the receptor when bound to different classes of ligands. This study represents one of the first attempts, beside structure determination and MD simulations, to link the water network of interactions with the activation process of GPCRs.
In summary, our work has highlighted the importance of lipids for GPCR function. We have gained additional insights into bias agonism at the b2AR and GHSR, with important implications in the context of drug design. Our studies also unveiled the allosteric role of hydration during GPCR activation, only hypothesized so far. These results have been presented at international conferences and meetings both by the fellow and the supervisors. One publication, describing the importance of the hydration network, is already available as open access while a second manuscript is in preparation.
Our results are of great interest in the context of drug design. For what concerns the b2AR, there is the need for better tolerated and safer drugs to prevent heart failure, the most common cause of death in the western countries. To achieve this goal we need more selective drugs, that only target one receptor subtype, and at the same time bias drugs, that only activate one signaling pathway. The compounds we have identified in our study are very selective for the b2AR and show bias for the hinibitory G protein Gi. They can be used as scaffolds to design the next generation of b2AR drugs.
The GHSR is a very interesting pharmacology target, implicated in various biological processes such as energy homeostasis, food intake and hormones secretion. GHSR is a main target for the treatment of obesity, but despite intense research no compounds have been identified yet to target this receptor. Issues in identifying such compounds include scarce drugs bioavailability and unexpected side effects. Additionally, the pharmacology of the GHSR is only partially understood. Our investigations aim at a better understanding of the GHSR as a system, to delineate the important aspects of its modulation in terms of ligands, lipids and allosteric modulation. Our findings deepen our knowledge of the conformational changes experience by GHSR during activation. In particular, bias ligands seem to drive distinct receptor conformational changes. These different receptor conformations are likely the key to GPCR modulation and their characterization is of fundamental interest for the design of future drugs.