EVIDENCE FOR A C-TERMINAL TURN IN PBAN - AN NMR AND DISTANCE GEOMETRYSTUDY

The solution conformation of the pheromone biosynthesis activating neu ropeptide (PBAN) of the moth Helicoverpa zea has been determined using homonuclear two-dimensional nuclear magnetic resonance techniques and distance geometry-restrained energy minimization. The insect peptide hormone showed a random distribution of conformers in aqueous solution , whereas in a less polar medium of trifluoroethanol and water, a reor dering process was observed. In particular, the C-terminal region (Phe -Ser-Pro-Arg-Leu-NH2) adopts a type I' beta-turn conformation, residue s 20-27 are in a helix conformation, and residues 1-19 exhibit a high degree of flexibility. Direct observation of the C-terminal beta-turn configuration of PBAN is consistent with a previous report that showed a rigid, cyclic analog of the C-terminal pentapeptide of PBAN retaine d pheromonotropic activity [Nachman, R.J., Kuniyoshi, H., Roberts, V.A ., Holman, G.M. & Suzuki, A. (1993). Biochem. Biophys. Res. Commun. 66 1-666]. Furthermore, our results show no interaction between the C-ter minal turn and the rest of the polypeptide chain, thus providing furth er evidence that the C-terminal turn is indeed the important conformat ion recognized by the PBAN receptor. (C) Munksgaard 1996.