Abstract by Daniel Philip Middleton

G-protein coupled receptors (GPCRs) comprise the largest protein superfamily in the human genome, accounting for approximately one third of all protein-coding genes. GPCRs respond to a diverse array of ligands and mediate their intracellular responses by coupling to and activating G-proteins, which initiate downstream signalling partners. While there are in the order of 800 GPCRs, there exist only a handful of G-protein subtypes; most GPCRs signal via several subtypes of G-protein and all G-proteins couple successfully to many different GPCRs. Despite much research into the problem, what determines this receptor--G-protein subtype specificity remains unknown.

In this thesis, we identify several amino-acid residues in a few GPCRs that are key for determining which G-proteins these receptors interact with. Radioligand competition binding and [³H]GDP release assays performed on large numbers of combinations of wild-type and mutant receptor:G-protein pairings enabled us to identify main areas of GPCR residues that inuence G-protein selectivity determination. Our results provide a strong and detailed basis for how GPCR:G-protein selectivity is determined on a molecular level and allow us to propose an outline of a model for how GPCRs enable or prevent coupling among three different G-protein subtypes.

While work is ongoing to complete models of selectivity encoding, we expect that our results will provide a solid basis upon which future research can build in order to decode this extremely complex and nuanced challenge.