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Selective ligand-induced stabilization of active and desensitized parathyroid hormone type 1 receptor conformations
Alessandro Bisello1, Michael Chorev, Michael Rosenblatt
1Department of Medicine, Division of Endocrinology and Metabolism, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA. biselloa@msx.dept-med.pitt.edu
Abstract:
For many G protein-coupled receptors, agonist-induced activation is followed by desensitization, internalization, and resensitization. In most cases, these processes are dependent upon interaction of agonist-occupied receptor with cytoplasmic beta-arrestins. The ligand-induced intramolecular rearrangements of the receptor responsible for the desensitized versus active conformational states, which dictate both the pharmacological properties of ligands and the biological activity of G protein-coupled receptors, have not been fully elucidated. Here, we identify specific interactions between parathyroid hormone (PTH)-related protein and the human PTH type 1 receptor (PTH1Rc) and the related receptor conformational changes that lead to beta-arrestin-2-mediated desensitization. PTH-related protein analogs modified at position 1 induced selective stabilization of the active G protein-coupled state of the receptor, resulting in lack of beta-arrestin-2 recruitment to the cell membrane, sustained cAMP signaling, and absence of ligand-receptor complex internalization. Mechanistically, the ligands modified at position 1, interacting with the extracellular end of helix VI of PTH1Rc, produced a translocation of transmembrane helices V and VI that differed from that induced by the cognate agonist, resulting in significantly different conformations of the third intracellular loop. These results show how specific interactions between PTH1Rc and its ligands may stabilize distinct conformational states, representing either the active G protein-coupled or a desensitized beta-arrestin-coupled receptor state. In addition, they establish that sustained biological activity of PTH1Rc may be induced by appropriately designed agonist ligands.
Insights
Specific interactions between parathyroid hormone (PTH)-related protein and the PTH type 1 receptor (PTH1Rc) stabilize distinct receptor states. Appropriately designed PTH analogs can sustain PTH1Rc biological activity by preventing desensitization.
Area of Science:
- Biochemistry
- Molecular Pharmacology
- Structural Biology
Background:
- G protein-coupled receptors (GPCRs) undergo desensitization and internalization after agonist activation, often involving beta-arrestins.
- Understanding ligand-induced receptor conformational changes is crucial for GPCR pharmacology and biological activity.
- The specific mechanisms driving distinct active versus desensitized states of GPCRs remain incompletely understood.
Purpose of the Study:
- To elucidate the specific interactions between parathyroid hormone (PTH)-related protein and the human PTH type 1 receptor (PTH1Rc).
- To identify receptor conformational changes leading to beta-arrestin-2-mediated desensitization.
- To investigate how ligand modifications influence receptor signaling and downstream effects.
Main Methods:
- Investigated interactions between PTH-related protein analogs and the human PTH type 1 receptor (PTH1Rc).
- Analyzed receptor conformational changes using structural and signaling assays.
- Assessed beta-arrestin-2 recruitment, cAMP signaling, and ligand-receptor complex internalization.
Main Results:
- PTH-related protein analogs modified at position 1 selectively stabilized the active G protein-coupled state of PTH1Rc.
- These modified analogs prevented beta-arrestin-2 recruitment, leading to sustained cAMP signaling and no internalization.
- Ligand interaction with helix VI of PTH1Rc induced distinct transmembrane helix V and VI translocations and altered third intracellular loop conformations.
Conclusions:
- Specific ligand-receptor interactions dictate the stabilization of either the active G protein-coupled or the desensitized beta-arrestin-coupled state of PTH1Rc.
- Tailored agonist ligands can be designed to induce sustained biological activity of PTH1Rc by preventing desensitization.