Residue 19 of the parathyroid hormone: structural consequences.
Residue 19 of the parathyroid hormone (PTH) has been shown to play an important role in both binding to and activation of the PTH receptor; specifically, Arg(19)-containing analogues have improved biological function over similar Glu(19) peptides [Shimizu et al. (2002) Biochemistry 41, 13224-13233]. Additionally the juxtamembrane portion of the receptor is involved in the different biological responses. Here, we determine the conformational preferences of PTH analogues to provide a structural basis for their biological actions. On the basis of circular dichroism results, the Arg(19) --> Glu(19) mutations within the context of both PTH(1-20) and PTH(1-34) analogues lead to increases in helix content, ranging from a 8-15% increase. High-resolution structures as determined by (1)H NMR and NOE-restrained molecular dynamics simulations clearly illustrate the difference between Arg(19) and Glu(19)-PTH(1-20), particularly with the extent and stability of the C-terminal helix. The Arg(19)-containing analogue has a well defined, stable alpha-helix from Ser(4)-Arg(19), while the Glu(19) analogue is less ordered at the C-terminus. On the basis of these observations, we propose that position 19 of PTH(1-20) must be alpha-helical for optimal interaction with the juxtamembrane portion of the receptor. This mode of binding extends the current view of PTH binding (indeed ligand binding for all class B GPCRs), which invokes a bihelical ligand with the C-terminus of the ligand interacting with the N-terminus of the receptor (responsible for binding) and the N-terminus of the ligand interacting with the seven-helical bundle (leading to receptor activation).
Piserchio
Andrea
A
Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
Shimizu
Naoto
N
Gardella
Thomas J
TJ
Mierke
Dale F
DF
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D001120:Arginine / Q000737:chemistry / Q000235:genetics; D002942:Circular Dichroism; D003198:Computer Simulation; D018698:Glutamic Acid / Q000737:chemistry / Q000235:genetics; D008024:Ligands; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010281:Parathyroid Hormone / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000235:genetics / Q000502:physiology; D018016:Receptors, Parathyroid Hormone / Q000737:chemistry
D008024:Ligands; D010281:Parathyroid Hormone; D010446:Peptide Fragments; D018016:Receptors, Parathyroid Hormone; D018698:Glutamic Acid; D001120:Arginine