Poster Presentation The 47th Lorne Conference on Protein Structure and Function 2022

Structural insights into GLP-1R activation and allosteric modulation by non-peptidic ligands (#228)

Xin Zhang 1 2 , Matthew Belousoff 1 2 , Fabian Eisenstein 3 , Radostin Danev 3 , Patrick Sexton 1 2 , Denise Wootten 1 2
  1. ARC Centre for Cryo-electron Microscopy of Membrane , Monash University, Melbourne, Vic, Australia
  2. Drug Discovery Biology, Monash Univeristy, Melbourne, Vic, Australia
  3. Centre for Sport, Exercise and Life Sciences, Coventry University, Coventry, UK

The glucagon-like peptide 1 receptor (GLP-1R) is a well-established clinical target for type II diabetes. Several peptide agonists are clinically approved, but there remains substantial interest in the development of orally delivered drugs. A variety of GLP-1R non-peptidic agonists and positive allosteric modulators (PAMs) have been identified, however, how they bind and modulate GLP-1R function is poorly understood. We determined cryo-electron microscopy structures of GLP-1R-Gs complexes bound by three endogenous agonists (GLP-1, GLP-1(9-36)NH2, oxyntomodulin), two non-peptidic agonists (PF 06882961 and CHU-128) and three PAMs (compound 19, BETP and compound 2) bound either alone, or co-bound with endogenous peptide agonists. These structures reveal the binding sites for PF 06882961 and endogenous peptide agonists substantially overlap, whereas CHU-128 has more limited overlap with this site, adopting a unique binding mode with a more open receptor conformation at the extracellular face. Structural differences involving extensive water-mediated hydrogen bond networks could be correlated to functional data to understand how PF 06882961, but not CHU-128, can closely mimic the pharmacological properties of GLP-1. Compound 19 binds in an allosteric binding pocket at an interface between the top of TM1 and TM2, and also forms direct interactions with GLP-1(9-36)NH2 to stabilise its binding. Thus, this can explain the ability of compound 19 to selectively modulate the activity of this peptide, but not other endogenous peptides. Compound 2 and BETP bind to a distinct allosteric site at the intracellular end of TM6, where both compounds can modulate the signalling and regulatory events of the three endogenous agonists, but to different extents. The different PAMs induce distinct complex conformations and receptor conformational dynamics that can, in part, explain differences in their modulatory profiles. These findings will facilitate rational structure-based discovery of non-peptidic drugs targeting the GLP-1R and other related class B1 G protein-coupled receptors.