STRUCTURE AND PROTEIN-KINASE-C STIMULATING ACTIVITIES OF LACTAM ANALOGS OF HUMAN PARATHYROID-HORMONE FRAGMENT

Five analogues of human parathyroid hormone {hPTH-(20-34)-NH2, I; cycl e[Lys(26)-Asp(30)]-hPTH-(20-34)-NH2, II; cyclo[Glu(23)-Lys(26)]-hPTH-( 20-34)-NH2, III; cyclo[Lys(27)-Asp(30)]-hPTH-(20-34)-NH2, IV; and [Leu (27)]-hPTH-(20-34)-NH2, V} were tested for their ability to promote me mbrane-bound protein kinase C (PKC) activity in a rat osteosarcoma cel l line (ROS 17/2). Analogues I, II and V stimulated PKC activity in th e picomolar range, whereas analogues III and IV did not stimulate this activity at any concentration tested. The circular dichroism spectra in neutral, aqueous buffer showed an increase in alpha-helix in analog ues II, III and V as compared to I; this increase appeared to be in th e region of the cyclic lactam structure. Analogue IV did not adopt a h elical structure, even in the presence of 40% trifluoroethanol, a heli x-promoting solvent. The remaining analogues showed a three- to four-f old enhancement of alpha-helix in this solvent. Analogues II and III h ad increased retention times in reversed-phase chromatography, as comp ared to I and IV. This is consistent with a stabilization of amphiphil ic helix in analogues II and III compared with I and IV. The data sugg est that in the region bounded approximately by residues 24-32, an amp hiphilic alpha-helix is important for correct functional binding to th e PTH receptor. (C) Munksgaard 1994.