Understanding the activation mechanism of GLP-1R/GIPR by dual agonist Tirzepatide via molecular dynamics and protein-peptide binding.

GLP-1 has become a prime target for medical treatment due to its significant therapeutic efficacy. However, the activation mechanisms of class B1 GPCRs, including glucagon-like peptides (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), remain poorly understood. This study focuses on understanding the activation mechanisms of the GLP-1 receptor (GLP-1R) by investigating its conformational changes from activated/inactivated to inactivated/activated states. By analyzing the dynamic conformational changes of the receptor during activation, a closure-open transition in the extracellular domain (ECD) and a movement trend of the transmembrane helices are observed, which indicates a similarity to the activation mechanism of class A GPCRs. Furthermore, the binding characteristics of a dual agonist Tirzepatide (LY3298176) is studied in detail and it is revealed that the conserved residues contribute in a similar fashion toward binding to both GLP-1R and GIPR. Mutations in non-conserved residues in Tirzepatide affect the binding affinity, with C-terminal mutations weakening the binding affinity toward GLP-1R, while N-terminal mutations enhancing the affinity to GIPR, resulting in a biased binding mode. These findings enriched our fundamental understanding of GLP-1R/GIPR activation and provided theoretical guidance for the design and development of future peptide-based agonists and offer insights into the optimization of other dual or multi-target agonists.