PYY3-36 is a biopharmaceutical antiobesity agent under development as well as an endogenous satiety hormone, which is generated by dipeptidyl peptidase-IV digestion of polypetide YY (PYY), and in contrast to the parent hormone, PYY is highly selective for the Y2 versus the Y1 receptor. NMR analysis revealed a highly ordered, back-folded structure for human PYY in aqueous solution similar to the classical PP-fold structure of pancreatic polypeptide. The NMR analysis of PYY3-36 also showed a folded structure resembling a PP-fold, which however was characterized by far fewer long distance NOEs than the PP-fold observed in the full-length peptide. This suggests that either a conformational change has occurred in the N-terminal segment of PYY3-36 or that this segments is characterized by larger dynamics. The study supports the notion that the PP-fold is crucial for establishing simultaneous interactions with two subsites in the receptor for binding of, respectively, the N- and C-terminal ends of PYY. The Y2 receptor only requires recognition of the C-terminal segment of the molecule as displayed by the Y2 selective PYY3-36.