| Summary: | G-protein coupled receptors (GPCRs) are a diverse superfamily of membrane proteins. They have a wide range of physiological roles and include many successful drug targets. Sequencing of the human genome has revealed a distinct subfamily of GPCRs known as Adhesion GPCRs. These receptors possess unusually large extracellular N-terminal domains which are believed to be involved in cell-cell adhesion. Few data are available which demonstrate that these receptors are able to couple to G-proteins, their classification as GPCRs is primarily based on homology and predicted topology. These receptors are also mainly orphans. This investigation aims to demonstrate G-protein coupling of Adhesion GPCR members and use this coupling to aid de-orphanisation and pharmacological targeting. In this study, a selection of Adhesion GPCRs are expressed in a range of yeast (S. cerevisiae) strains each harbouring different mammalian-yeast chimeric G-proteins. Constitutive coupling of four different Adhesion GPCRs to the chimeric G-proteins is observed via a reporter gene assay. The chimeric G-proteins used represent the human complement, allowing prediction of the G-protein specificities of these receptors. This yeast assay is then used for high throughput screening to identify both potentially native ligands and inhibitors/potential therapeutic compounds. Following analysis in yeast, the Adhesion GPCRs CD97 and EMR2 were expressed in mammalian HEK293 cells where they also displayed constitutive activity when co-expressed with the appropriate Go. subunits (GaJ6).This constitutive activity is strong and mirrors the G-protein specificities seen in yeast. Using this assay, the effects of candidate CD97 and EMR2 ligands were assessed, their putative binding sites
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