A salt bridge between Arg-20 on parathyroid hormone (PTH) and Asp-137 on the PTH1 receptor is essential for full affinity

High-resolution crystal structure of parathyroid hormone 1 receptor in complex with a peptide agonist

Parathyroid hormone 1 receptor (PTH1R) is a class B multidomain G-protein-coupled receptor (GPCR) that controls calcium homeostasis. Two endogenous peptide ligands, parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP), activate the receptor, and their analogs teriparatide and abaloparatide are used in the clinic to increase bone formation as an effective yet costly treatment for osteoporosis. Activation of PTH1R involves binding of the peptide ligand to the receptor extracellular domain (ECD) and transmembrane domain (TMD), a hallmark of class B GPCRs. Here, we present the crystal structure of human PTH1R in complex with a peptide agonist at 2.5-Å resolution, allowing us to delineate the agonist binding mode for this receptor and revealing molecular details within conserved structural motifs that are critical for class B receptor function. Thus, this study provides structural insight into the function of PTH1R and extends our understanding of this therapeutically important class of GPCRs.

Large Scale Synthetic Site Saturation GPCR Libraries Reveal Novel Mutations That Alter Glucose Signaling

Site saturation mutagenesis (SSM) is a powerful mutagenesis strategy for protein engineering and directed evolution experiments. However, limiting factors using this method are either biased representation of variants, or limiting library size. To overcome these hurdles, we generated large scale targeted synthetic SSM libraries using massively parallel oligonucleotide synthesis and benchmarked this against an error-prone (epPCR) library. The yeast glucose activated GPCR-Gpr1 was chosen as a prototype to evolve novel glucose sensors. We demonstrate superior variant representation and several unique hits in the synthetic library compared to the PCR generated library. Application of this mutational approach further builds the possibilities of synthetic biology in tuning of a response to known ligands and in generating biosensors for novel ligands.