期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 116, 期 8, 页码 3294-3299出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1814670116
关键词
PTH; PTH receptor; GPCR signaling; Ca2+ allosterism; endosomal cAMP signaling
资金
- National Institute of Diabetes and Digestive and Kidney Disease
- National Institute of General Medical Sciences of the US National Institutes of Health [R01-DK102495, R01-DK111427, R01-DK116780, T32-GM008424]
- Cotswold Foundation
- Department of Pharmacology and Chemical Biology of the University of Pittsburgh
- Vascular Medicine Institute of the University of Pittsburgh
- Hemophilia Center of Western Pennsylvania
- Institute for Transfusion Medicine
- Basic Science Research Program of the National Research Foundation of Korea [NRF-2013R1A1A1A05005629]
- Korea Research-Driven Hospitals [FRD2014-04]
The parathyroid hormone (PTH) and its related peptide (PTHrP) activate PTH receptor (PTHR) signaling, but only the PTH sustains GS-mediated adenosine 3',5'-cyclic monophosphate (cAMP) production after PTHR internalization into early endosomes. The mechanism of this unexpected behavior for a G-protein-coupled receptor is not fully understood. Here, we show that extracellular Ca2+ acts as a positive allosteric modulator of PTHR signaling that regulates sustained cAMP production. Equilibrium and kinetic studies of ligand-binding and receptor activation reveal that Ca2+ prolongs the residence time of ligands on the receptor, thus, increasing both the duration of the receptor activation and the cAMP signaling. We further find that Ca2+ allostery in the PTHR is strongly affected by the point mutation recently identified in the PTH (PTHR25C) as a new cause of hypocalcemia in humans. Using high-resolution and mass accuracy mass spectrometry approaches, we identified acidic clusters in the receptor's first extracellular loop as key determinants for Ca2+ allosterism and endosomal cAMP signaling. These findings coupled to defective Ca2+ allostery and cAMP signaling in the PTHR by hypocalcemia-causing PTHR25C suggest that Ca2+ allostery in PTHR signaling may be involved in primary signaling processes regulating calcium homeostasis.
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