Direct identification of two contact sites for parathyroid hormone (PTH) in the novel PTH-2 receptor using photoaffinity cross-linking.
Direct examination of the interacting sites between PTH and the human PTH2 receptor (PTH2R) was conducted by photoaffinity cross-linking followed by protein digestion and mapping of the radiolabeled photoconjugated receptor. Photoreactive analogs of PTH, individually substituted with an L-p-benzoylphenylalanine (Bpa) at each of the first 6 N-terminal positions, were pharmacologically evaluated in cells stably expressing recombinant PTH2R. One highly bioactive analog, [Bpa1,Nle8,18,Arg13,26,27,L-2-Nal23,Tyr34]PTH-(1-34)NH 2 (Bpa1-PTH), was chosen for cross-linking studies. In addition, a PTH analog in which the photoreacive moiety is at the mid-region position 13 (K13) was demonstrated to be bioactive, then cross-linked to PTH2R. The minimal digestion-restricted domain containing the contact site ("contact domain") for 125I-Bpa1-PTH is in the sixth transmembrane domain and part of the third extracellular loop, spanning residues Ser364-Met395 of the receptor. This domain was further confirmed and refined by cross-linking 125I-Bpa1-PTH to two receptor mutants, PTH2R[V380M]- and PTH2R[V380M,M395L]-receptors. Treatment of the cross-linked conjugates with cyanogen bromide identified a single amino acid (position 380) as the putative contact point. The contact domain for 125I-K13 is located in the N-terminal extracellular tail of the receptor (in the C-terminal portion) and spans Gln138-Met147. Further validation of this contact domain was accomplished by photocross-linking to point-mutated PTH2R[K137R] receptor. Previous studies in which PTH analogs were cross-linked to human PTH/PTHrP receptor (PTH1R) identified Met425 and Phe173-Met189 as the contact sites for Bpa1-PTH and K13, respectively. These studies demonstrate that both receptor subtypes, PTH1- and PTH2-receptors, use analogous sites for interaction with positions 1 and 13 in PTH.
Behar
V
V
Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
Bisello
A
A
Rosenblatt
M
M
Chorev
M
M
D000818:Animals; D019556:COS Cells; D002460:Cell Line; D003432:Cross-Linking Reagents; D006801:Humans; D008024:Ligands; D010281:Parathyroid Hormone / Q000737:chemistry / Q000378:metabolism*; D010449:Peptide Mapping; D019920:Photoaffinity Labels; D044183:Receptor, Parathyroid Hormone, Type 2; D018016:Receptors, Parathyroid Hormone / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D003432:Cross-Linking Reagents; D008024:Ligands; D010281:Parathyroid Hormone; D019920:Photoaffinity Labels; D044183:Receptor, Parathyroid Hormone, Type 2; D018016:Receptors, Parathyroid Hormone; D011994:Recombinant Proteins