SOLUTION STRUCTURE AND ADENYLYL-CYCLASE STIMULATING ACTIVITIES OF C-TERMINAL TRUNCATED HUMAN PARATHYROID-HORMONE ANALOGS

Analogues of human parathyroid hormone (hPTH) truncated at the C-termi nal end have been studied for adenylyl cyclase (AC) activity and for s olution conformation by circular dichroism (CD) spectroscopy. Analogue s of hPTH-(1-34)-NH2, containing the first 28-31 residues, had only a slightly diminished ability to stimulate AC in rat osteosarcoma (ROS) cells as compared to that of the parent analogue. CD data on hPTH-(16- 34)-NH2 and C-terminal deletion mutants of hPTH-(1-34)-NH2 supported t he presence of a partially stable alpha-helix over residues 17-28. A c arboxyl-terminal mutant, hPTH-(1-30)-OH, showed both reduced helix and greatly reduced AC-stimulating activity as compared to the correspond ing amide analogue. In contrast, both of these analogues, in the prese nce of palmitoyloleoylphosphatidylserine (POPS) vesicles, showed an eq ual stabilization of alpha-helix. All other analogues showed at least some enhancement of alpha-helix in the presence of POPS. However, both in neutral, aqueous buffer and in POPS, the relative amount of alpha- helix decreased greatly as the peptide was shortened below the 1-28 se quence. These data provide additional support for an amphiphilic alpha -helix over residues 21-28 being the conformation for receptor binding of hPTH for stimulation of AC activity. Modeling human parathyroid ho rmone-related peptide as an alpha-helix over this same region, and com parison to hPTH, suggests that both may bind via the hydrophobic face to the receptor.