Lipid sensitivity of the GPR132 receptor
The pH sensitive receptors are a group of four phylogenetically related G protein coupled receptors (GPCRs). The prototypical member of this family, GPR68, is activated by low pH extracellular conditions. However, GPR132 does not contain histidine residues at equivalent positions and is likely not to be activated by acid. GPR132 is described by the International Union of Basic and Clinical Pharmacology (IUPHAR) as an orphan GPCR, although there have been several reports linking it to activation by lipid molecules. GPR132 has been linked to the pathologies of inflammation, nociception and cancer. Therefore, an understanding of the molecular mechanisms which regulate this receptor is important to be able to devise strategies to restore homeostasis and alleviate disease. This study utilises different cell based assay platforms to demonstrate activation of GPR132 by two distinct groups of endogenous lipid; oxidised free fatty acid and N-acyl glycine. Both groups are found to activate GPR132 mediated downstream signalling pathways at varying magnitudes, perhaps explaining the different biological activities of these separate molecular families. Further computational modelling were used to identify a binding site for these ligands and validated using receptor mutagenesis. Interestingly, mutation of a highly conserved residue on transmembrane domain 5 was found to switch full agonist behaviour of a synthetic ligand towards an inverse agonist. Altogether, the experiments outlined in this thesis may prove useful in the design of potent antagonists for this receptor.
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