Phase-plate cryo-EM structure of a biased agonist-bound human GLP-1 receptor-Gs complex

The class B glucagon-like peptide-1 (GLP-1) G protein-coupled receptor is a major target for the treatment of type 2 diabetes and obesity(1). Endogenous and mimetic GLP-1 peptides exhibit biased agonism-a difference in functional selectivity-that may provide improved therapeutic outcomes1. Here we describe the structure of the human GLP-1 receptor in complex with the G protein-biased peptide exendin-P5 and a G alpha(s) heterotrimer, determined at a global resolution of 3.3 angstrom. At the extracellular surface, the organization of extracellular loop 3 and proximal transmembrane segments differs between our exendin-P5-bound structure and previous GLP-1-bound GLP-1 receptor structure(2). At the intracellular face, there was a six-degree difference in the angle of the G alpha(s)-alpha 5 helix engagement between structures, which was propagated across the G protein heterotrimer. In addition, the structures differed in the rate and extent of conformational reorganization of the G alpha(s) protein. Our structure provides insights into the molecular basis of biased agonism.