EFFECTS OF COVALENT DIMERIZATION ON THE STRUCTURE AND FUNCTION OF THECARBOXY-TERMINAL FRAGMENT OF NEUROPEPTIDE-Y

To determine whether or not the dimeric structure of neuropeptide Y (N PY) that is found in solution is necessary for its function, we invest igated the effects of covalent dimerization on the structure and funct ion of NPY using the carboxy-terminal fragment, NPY(12-36), in which r esidues 12 and 31 (located at both ends of alpha-helical region) were replaced by Cys residues. Among the three species (the parallel dimer, the anti-parallel dimer, and the intramolecularly cross-linked monome r) obtained by oxidation of the fragment, the anti-parallel dimer was pre-dominant. NMR analysis showed that both parallel and anti-parallel dimers had alpha-helices similar to that of intact NPY, suggesting th at covalent dimerization might have little effect on the helical struc ture. A binding assay with Y2 receptors on porcine hippocampal membran es revealed that the IC50 value of the anti-parallel dimer was almost the same as that of NPY(13-36), which is known as a Y2-specific ligand . By contrast, the binding by the parallel dimer was weaker by more th an one order of magnitude. Our results suggest that the formation of d imers of NPY is not essential for binding to the receptor. (C) 1997 Ac ademic Press.