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Abstract
Over 100 orphan G protein-coupled receptors (GPCRs) are yet to be paired with their endogenous ligand. As such, they represent a vast untapped resource for drug discovery. Therefore, identifying ligands for these orphan receptors is crucial for the exploration of their physiological and pharmacological relevance. One such orphan is GPR37L1, a potential mediator of cardiovascular homeostasis. In this thesis, GPR37L1 was found to be predominantly a constitutively active Gαs-coupled receptor and that metalloprotease cleavage of GPR37L1’s N-terminus regulated its signalling capabilities. This thesis also introduced GPCR-CoINPocket, a new method for orphan receptor ligand discovery. GPCR-CoINPocket (Contact-Informed Neighbouring Pocket) was first designed to improve recognition of known pharmacological similarities, or off-target activity amongst Class A GPCRs from a binding pocket perspective. This was achieved by focusing on specific residue positions in the ligand binding pocket that were interaction hotspots, as observed in crystallographically-characterised GPCRs. This was extended to prospectively predict binding site-similar receptors for all orphan receptors, including GPR37L1. GPCR-CoINPocket predicted the bombesin, orexin and neuropeptide S receptors to be most similar to GPR37L1, and not the phylogenetically related endothelin receptors, which guided and narrowed the search for GPR37L1 surrogate ligands. Other approaches were also used to identify GPR37L1 ligands, including traditional ligand screening and in silico ligand screening with an unrefined GPR37L1 homology model. The surrogate ligands identified with these various approaches will provide the necessary stepping-stone to explore the therapeutic potential of GPR37L1; the identified ligands can now be used to refine homology models for a second iteration of virtual ligand screening, as well as facilitate parallel in vitro and in vivo studies. The endogenous ligand for GPR37L1 remains elusive.