A salt bridge between Arg-20 on parathyroid hormone (PTH) and Asp-137 on the PTH1 receptor is essential for full affinity.
Parathyroid hormone (PTH) acts via the receptor PTH1 and plays an important role in calcium homeostasis. PTH's interaction with the N-terminal domain of PTH1 is mediated in part by Arg-20 on the peptide which forms a number of interactions with the receptor: a charge-charge interaction with Asp-137; hydrogen bonds with the backbone of Asp-29 and Met-32; and hydrophobic interactions with Met-32 and Gln-37. The aim of this work was to establish the importance of the charge-charge interaction through the combined use of modified peptide ligands, site-directed mutations of the receptor, and pharmacological assays. The substitution of Arg-20 with norleucine resulted in a 50-fold reduction in potency at PTH1 and Asp-137-Glu while, in contrast, both Asp-137-Asn and Asp-137-Ala receptors were largely insensitive to this ligand modification. The effect of this removal of the positive charge as position 20 could be partially rescued at PTH1 and Asp-137-Glu, but not Asp-137-Asn and Asp-137-Ala, through a substitution of peptide position 20 with ornithine. The latter two receptors, which have no negative charge at position 137, displayed potency for PTH that was reduced by 40- and 117-fold, respectively. These data demonstrate that a negative charge at residue-137 is important for interacting with ligands containing a positive charge at residue-20, and that the Arg-20 interaction with Asp-137, observed in the crystal structure of the isolated N-terminal domain of PTH1, is likely to be present in the full length receptor where it provides an important affinity- and potency-generating interaction through a salt bridge.
['Weaver|Richard E|RE|', 'Wigglesworth|Mark J|MJ|', 'Donnelly|Dan|D|']
D001120:Arginine D001224:Aspartic Acid D057809:HEK293 Cells D006801:Humans D010281:Parathyroid Hormone D020836:Protein Structure, Quaternary D017434:Protein Structure, Tertiary D044168:Receptor, Parathyroid Hormone, Type 1 D055672:Static Electricity
Parathyroid hormone PTH Receptor Agonist GPCR Osteoporosis