THE CONTRIBUTION OF HELICAL POTENTIAL TO THE IN-VITRO RECEPTOR-BINDING ACTIVITY OF A NEUROPEPTIDE-Y N-TERMINAL DELETION FRAGMENT

In its dimeric form neuropeptide Y (NPY) folds into a compact structur e in which the antiparallel oriented proline and alpha-helices apparen tly associate to form a primitive hydrophobic core. To investigate the contribution of helical stability to the receptor binding activity of NPY and its N-terminal deletion fragments, we synthesized and studied the solution conformational properties and in vitro activities of NPY , N(alpha)-acetyl-NPY2-36, NPY15-36, N(alpha)-propionyl-NPY15-36, and N(alpha)-succinyl-NPY15-36. NPY15-36 is significantly less helical tha n both NPY and N(alpha)-acetyl-NPY2-36, and this decreased helical pot ential is attributed to the absence of the intramolecular stabilizing interactions afforded by the proline helix in the latter analogues. Ho wever, in accord with the helix dipole model, the helical potential of NPY15-36 is significantly increased by N-terminal succinylation, wher eas propionylation has no effect. In addition to an increase in helica l potential, N(alpha)-succinyl-NPY-15-36 is 2.5 and 4.6 times more act ive than NPY15-36 and N(alpha)-propionyl-NPY15-36, respectively, and i s equipotent with N(alpha)-acetyl-NPY2-36 in displacing 1 n M [H-3]-NP Y from specific binding sites in rat brain membranes. The demonstratio n of a positive correlation between % alpha-helix content and in vitro binding activity suggests that the helical potential of N-terminal NP Y deletion fragments contributes to their in vitro activity in the rat brain, and that a second role of the proline helix might be to stabil ize the receptor-active conformation of the NPY alpha-helix. (C) 1993 John Wiley & Sons, Inc.