Aptamers for targeting Class B1 GPCRs and as modulators of receptor-induced cell signalling

BBSRC strategic theme: Bioscience for an integrated understanding of health

Aptamers are single stranded oligonucleotides with defined secondary structures. They are raised against select targets by Systematic Evolution of Ligands by Exponential enrichment (SELEX), resulting in high affinity and selectivity for their chosen target and allowing aptamers to gain much traction as alternatives to antibodies in the field of theranostics. G protein-coupled receptors (GPCRs) are transmembrane proteins that bind extracellular agonists, then transduce these signals across the plasma membrane to activate intracellular signalling cascades via G proteins and -arrestins. Class B1 GPCRs respond to peptide hormones and have substantial extracellular domains to facilitate the binding of their agonist ligands and subsequent conformational shifts that allow transmembrane signal transduction. This large extracellular region could act as a large surface across which aptamers may form extensive and selective interactions without need to cross the plasma membrane. Few aptamers have been raised against GPCRs, with only one Class B1 GPCR having been targeted: the glucagon receptor (GCGR). This GPCR mediates the hyperglycaemic effects of glucagon in the pancreas. Even fewer of these GPCR-targeting aptamers have been characterised in their ability to affect GPCR signalling; however, aptamers raised against the 2 adrenoceptor are selective for distinct conformational states of this receptor. This suggests that aptamers could drive GPCRs into receptor states with unique signalling profiles, allowing for tight control of target receptor signalling. For disease-implicated receptors, this could prevent pathogenic signalling and encourage health-promoting signalling pathways. The beginning of this project will investigate the pharmacological effects of the known GCGR-targeting aptamer. This will utilise bioluminescence resonance energy transfer (BRET)-based assays, for example using labelled G...