NOVEL MODIFIED CARBOXY-TERMINAL FRAGMENTS OF NEUROPEPTIDE-Y WITH HIGH-AFFINITY FOR Y-2-TYPE RECEPTORS AND POTENT FUNCTIONAL ANTAGONISM AT AY-1-TYPE RECEPTOR

Peptide analogs of neuropeptide Y (NPY) with a Tyr-32 and Leu-34 repla cement resulted in the decapeptide TyrIleAsnLeuIleTyrArgLeuArgTyr-NH2 (9; Table 1) and a 3700-fold improvement in affinity at Y-2 (rat brain ; IC50 = 8.2 +/- 3 nM) receptors when compared to the native NPY(27-36 ) C-terminal fragment. In addition, compound 9 was an agonist at Y-1 ( human erythroleukemia (HEL) cell; ED(50) = 8.8 +/- 0.5 nM) receptors w ith potency comparable to that of NPY(1-36) (ED(50) = 5 nM). Molecular dynamics and H-1-NMR were used to propose a solution structure of dec apeptide 9 and for subsequent analog design. The replacement of Leu wi th Pro at position 4 of decapeptide 9 afforded an antagonist of NPY in PILL cells (18, TyrIleAsnProIleTyrArgLeuArgTyr-NH2; IC50 = 100 +/- 5 nM). Deletion of the N-terminal tyrosine of 18 resulted in a 10-fold i mprovement in antagonistic activity with a parallel 4-fold decrease in Y-2 affinity. This potent antagonist may provide further insight into the physiological role(s) for NPY in the mammalian and peripheral ner vous system.