Electrostatic Interactions with Extracellular Loop 1 Modulate Hormone-Specific Changes in Parathyroid Hormone 1...

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• The parathyroid hormone 1 receptor (PTH1R), a G protein-coupled receptor (GPCR), is crucial in bone and kidney physiology.
• PTH1R is activated by parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP), modulating downstream signaling via Gs and Gq G proteins.
• The receptor's extracellular loop 1 (ECL1) is unusually long and implicated in allosteric modulation, but its precise regulatory role remains unclear.

Purpose of the Study:

• To investigate the functional role of ECL1 in PTH1R-mediated G protein binding and downstream signaling.
• To elucidate how ECL1 influences the differential signaling responses to PTH and PTHrP.

Main Methods:

• Generation of a PTH1R mutant lacking ECL1 (ΔECL1 PTH1R).
• Assessment of G protein (Gs and Gq) binding and activation in response to PTH and PTHrP using the WT and ΔECL1 PTH1R.
• Analysis of downstream signaling pathways modulated by hormone-receptor interactions.

Main Results:

• The ΔECL1 PTH1R mutant showed increased Gs interactions and signaling for PTH, but decreased for PTHrP, compared to WT.
• Both PTH and PTHrP exhibited increased Gq interactions and signaling with the ΔECL1 PTH1R mutant compared to WT.
• Hormone-specific Gs signaling regulation is linked to C-terminal charged residues and ECL1's electrostatic interactions with PTH and PTHrP.

Conclusions:

• ECL1 plays a critical role in differentially regulating PTH1R signaling pathways activated by PTH and PTHrP.
• ECL1's electrostatic properties influence hormone binding and subsequent G protein activation, particularly for Gs signaling.
• Understanding ECL1's mechanism provides insights into PTH1R function and potential therapeutic targets for related conditions.