Structure-Function Relationship Investigations of Neuropeptide Y Bound to Hydrated Lipid Bilayers

Abstract

Neuropeptide Y (NPY) is a neuroendocrinic peptide which belongs to the neuropeptide Y family. It activates Y-receptors, which are G-protein coupled receptors (GPCRs), and regulates various physiological processes. Furthermore, NPY and some of its fragments have antimicrobial and immunochemical properties. Several biophysical studies of NPY in the presence of model membranes indicate that it interacts strongly with various lipids. Notably, the structure of micelle-bound NPY has provided insights about how the so-called membrane catalysis model of Schwyzer applies to NPY. This model proposes that the membrane induces a “bio-active conformation” of the peptide that has the required orientation to bind the receptor selectively. Characterizing the structural features of NPY under physiologically relevant conditions is important to better understand its multiple functions. Since variations in the lipid composition of biological membranes can have drastic effects on the activity of NPY and its fragments, we have used a combination of solid-state NMR techniques to probe these peptides under changing conditions. In order to investigate the structure, dynamics, topology and depth of insertion of the peptides in the membrane-bound state, we have incorporated the peptides in various aligned lipid mixtures and collected 15N and 31P solid-state NMR spectra from the peptides and lipids, respectively. Circular dichroism studies have also been performed to assess the global structures of the peptides under sample conditions mirroring the ones used for the NMR studies. Finally, we have investigated the antimicrobial activity of the peptides on Gram-positive and Gram-negative bacteria. The results of these studies could be significant in understanding the modes of action of NPY as a multifunctional peptide active at various bacterial and mammalian lipid membranes.