Evidence that the PTH receptor binding site on PTHrP(1-34) can hinge at Arg19/Arg20.

The structure of the biologically-active mutant of human parathyroid hormone related protein (residues 1-34) containing an Ala substituted for a His in position 9 reveals two segments of helix extending from Glu4 to Lys13 and from Phe22 to Ala34, with a reverse turn from Gln16 to Arg19. The C-terminal region contains the bulk of the PTH receptor binding site in an amphipathic helix and is capable of hinging at Arg19/Arg20. The region of the molecule containing full antagonist properties is thus confined to the C-terminal helix.