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Towards Understanding the Free and Receptor Bound Conformation of Neuropeptide Y by Fluorescence Resonance Energy Transfer Studies

Despite a considerable sequence identity of the three mammalian hormones of the neuropeptide Y family, namely neuropeptide Y, peptide YY and pancreatic polypeptide, their structure in solution is described to be different. A so‐called pancreatic polypeptide‐fold has been identified for pancreatic polypeptide, whereas the structure of the N‐terminal segment of neuropeptide Y is unknown. This element is important for the binding of neuropeptide Y to two of its relevant receptors, Y1 and Y5, but not to the Y2 receptor subtype. In this study now, three doubly fluorescent‐labeled analogs of neuropeptide Y have been synthesized that still bind to the Y5 receptor with high affinity to investigate the conformation in solution and, for the first time, to probe the conformational changes upon binding of the ligand to its receptor in cell membrane preparations. The results obtained from the fluorescence resonance energy transfer investigations clearly show considerable differences in transfer efficiency that depend both on the solvent as well as on the peptide concentration. However, the studies do not support a pancreatic polypeptide‐like folding of neuropeptide Y in the presence of membranes that express the human Y5 receptor subtype.