Allosteric interactions in the parathyroid hormone GPCR-arrestin complex formation.

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Class B G-protein-coupled receptors (GPCRs) mediate diverse physiological processes.
• Peptide ligand binding to Class B GPCRs involves a complex, multi-step mechanism.
• The precise link between extracellular ligand binding and intracellular signaling, particularly receptor-arrestin interactions, remains incompletely understood.

Purpose of the Study:

• To elucidate the structural mechanisms underlying the two-step binding process of peptide ligands to Class B GPCRs.
• To investigate the specific interactions between parathyroid hormone (PTH) and the PTH type 1 receptor (PTHR) that lead to β-arrestin recruitment.
• To uncover the structural determinants governing PTHR-arrestin complex formation.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy
• Crosslinking coupled to mass spectrometry (XL-MS)
• Cellular signaling assays
• Computational modeling and simulations

Main Results:

• Initial binding of the PTH C-terminus to PTHR allosterically primes the receptor by constraining the N-terminal signaling epitope.
• A key PTH residue (His9) inserts into the PTHR transmembrane domain during the second binding step, allosterically mediating receptor-arrestin coupling.
• A conformational rearrangement in PTHR intracellular loop 3 facilitates favorable interactions with β-arrestin's finger loop, stabilizing the complex.
• The findings reveal cooperative ligand-receptor dynamics extending to other Class B GPCRs.

Conclusions:

• The two-step binding mechanism of PTH to PTHR involves sequential conformational changes that bridge extracellular ligand recognition with intracellular β-arrestin engagement.
• Structural insights into PTHR-arrestin complex formation highlight specific residues and conformational shifts critical for signal transduction.
• This study provides a framework for understanding ligand-receptor-arrestin interactions in Class B GPCRs and informs the design of novel therapeutics.