The parathyroid hormone type 1 receptor (PTH1R), a class B1 G protein-coupled receptor, plays critical roles in bone turnover and Ca2+ homeostasis. Teriparatide (PTH) and Abaloparatide (ABL) are terms as long-acting and short-acting peptide, respectively, regarding their marked duration distinctions of the downstream signaling. However, the mechanistic details remain obscure. Here, we report the cryo-electron microscopy structures of PTH– and ABL–bound PTH1R-Gs complexes, adapting similar overall conformations yet with notable differences in the receptor ECD regions and the peptide C-terminal portions. 3D variability analysis and site-directed mutagenesis studies uncovered that PTH–bound PTH1R–Gs complexes display less motions and are more tolerant of mutations in affecting the receptor signaling than ABL–bound complexes. Furthermore, we combined the structural analysis and signaling assays to delineate the molecular basis of the differential signaling durations induced by these peptides. Our study deepens the mechanistic understanding of ligand-mediated prolonged or transient signaling.

The parathyroid hormone type 1 receptor (PTH1R) is a class B1 G protein-coupled receptor (GPCR) that plays critical roles in bone turnover and Ca2+ homeostasis via mediating the actions of two distinct peptides, PTH and PTHrP. The major difference between the two endogenous peptides or their drugs analog, Teriparatide (PTH) and Abaloparatide (ABL), is their marked duration distinctions of the downstream signaling, a key determinant that is responsible for their distinct physiological or pharmacological properties. However, the mechanistic details underlying the distinct signaling behaviors remain obscure. Here, we report the cryo-electron microscopy (cryo-EM) structures of PTH and ABL–bound PTH1R-Gs complexes. Structural comparisons showed that the two structures adopt similar overall conformations yet with notable conformational differences in the ECD regions of the receptor and the C-terminal portion of the peptides. 3D variability analysis and site-directed mutagenesis studies uncovered that the long-acting peptides– (PTH and LA-PTH) bound PTH1R–Gs complexes display less motions and are more tolerant of mutations in affecting the receptor signaling than the short-acting ABL–bound complexes. In addition, we combined the structural analysis and signaling assays, along with prior studies to delineate the molecular basis of the differential signaling durations induced by these peptides. Collectively, these findings not only provide insights into the ligand recognition and specificity of the two distinct peptides but also deepen our understanding of the underlying mechanisms for their mediated prolonged or transient signaling.