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Turn-on switch in parathyroid hormone receptor by a two-step parathyroid hormone binding mechanism

Authors
  • Marián Castro
  • Viacheslav O. Nikolaev
  • Dieter Palm
  • Martin J. Lohse
  • Jean-Pierre Vilardaga
Publisher
National Academy of Sciences
Publication Date
Oct 18, 2005
Source
PMC
Keywords
Disciplines
  • Biology
License
Unknown

Abstract

Parathyroid hormone (PTH) and its related receptor (PTHR) are essential regulators of calcium homeostasis and bone physiology. PTH activates PTHR by interacting with a ligand-binding site localized within the N-terminal extracellular domain (the N-domain) and the domain comprising the seven transmembrane helices and the connecting extracellular loops (the J-domain). PTH binding triggers a conformational switch in the receptor, leading to receptor activation and subsequent cellular responses. The process of receptor activation occurs rapidly, within ≈1 s, but the binding event preceding receptor activation is not understood. By recording FRET between tetramethyl-rhodamine in PTH(1-34) and GFP in the N-domain of the receptor, we measured the binding event in real time in living cells. We show that the association time course between PTH(1-34) and PTHR involves a two-step binding process where the agonist initially binds the receptor with a fast time constant (τ ≈ 140 ms) and then with slower kinetics (τ ≈ 1 s). The fast and slow phases were assigned to hormone association to the receptor N- and J domains, respectively. Our data indicate that the slow binding step to the J-domain coincides with a conformational switch in the receptor, also monitored by FRET between the enhanced cyan fluorescent protein and the enhanced yellow fluorescent protein in the PTHR sensor, PTHR enhanced cyan fluorescent protein/enhanced yellow fluorescent protein (PTHRCFP/YFP). These data suggest that the conformational change that switches the receptor into its active state proceeds in a sequential manner, with the first rapid binding step event preceding receptor activation by PTH(1-34).

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