GSBS Student Publications

Title

Altered selectivity of parathyroid hormone (PTH) and PTH-related protein (PTHrP) for distinct conformations of the PTH/PTHrP receptor

GSBS Program

Biochemistry & Molecular Pharmacology

UMMS Affiliation

Graduate School of Biomedical Sciences

Date

9-18-2007

Document Type

Article

Medical Subject Headings

Animals; COS Cells; Cell Line; Cell Line, Tumor; Cercopithecus aethiops; Cyclic AMP; Fluorescence Resonance Energy Transfer; Kinetics; Humans; Luminescent Proteins; Luminescent Proteins; Parathyroid Hormone-Related Protein; Protein Binding; Protein Conformation; Receptors, Parathyroid Hormone; Recombinant Fusion Proteins; Transfection

Disciplines

Life Sciences | Medicine and Health Sciences

Abstract

PTH and PTHrP use the same G protein-coupled receptor, the PTH/PTHrP receptor (PTHR), to mediate their distinct biological actions. The extent to which the mechanisms by which the two ligands bind to the PTHR differ is unclear. We examined this question using several pharmacological and biophysical approaches. Kinetic dissociation and equilibrium binding assays revealed that the binding of [(125)I]PTHrP(1-36) to the PTHR was more sensitive to GTPgammaS (added to functionally uncouple PTHR-G protein complexes) than was the binding of [(125)I]PTH(1-34) ( approximately 75% maximal inhibition vs. approximately 20%). Fluorescence resonance energy transfer-based kinetic analyses revealed that PTHrP(1-36) bound to the PTHR more slowly and dissociated from it more rapidly than did PTH(1-34). The cAMP signaling response capacity of PTHrP(1-36) in cells decayed more rapidly than did that of PTH(1-34) (t(1/2) = approximately 1 vs. approximately 2 h). Divergent residue 5 in the ligand, Ile in PTH and His in PTHrP, was identified as a key determinant of the altered receptor-interaction responses exhibited by the two peptides. We conclude that whereas PTH and PTHrP bind similarly to the G protein-coupled PTHR conformation (RG), PTH has a greater capacity to bind to the G protein-uncoupled conformation (R(0)) and, hence, can produce cumulatively greater signaling responses (via R(0)-->RG isomerization) than can PTHrP. Such conformational selectivity may relate to the distinct modes by which PTH and PTHrP act biologically, endocrine vs. paracrine, and may help explain reported differences in the effects that the ligands have on calcium and bone metabolism when administered to humans.

Rights and Permissions

Citation: Mol Endocrinol. 2008 Jan;22(1):156-66. Epub 2007 Sep 13. Link to article on publisher's site

DOI of Published Version

10.1210/me.2007-0274

Related Resources

Link to Article in PubMed

Journal Title

Molecular endocrinology (Baltimore, Md.)

PubMed ID

17872377