Primary structures of PYY, [Pro34]PYY, and PYY-(3-36) confer different conformations and receptor selectivity

We synthesized PYY-(1-36) (nonselective between Y-1 and Y-2 receptor subtype agonists), [Pro(34)]-PYY (selective for Y-1), and PYY-(3-36) (selective for Y-2) to determine whether solution conformation plays a role in receptor subtype selectivity. The three peptides exhibited the expected specificities in displacing labeled PYY-(1-36) from cells transfected with Y-1 receptors (dissociation constants = 0.42, 0.21, and 1,050 nM, respectively) and from cells transfected with Y2 receptors (dissociation constants = 0.03, 710, and 0.11 nM, respectively) for PYY-(1-36), [Pro(34)]PYY, and PYY-(3-36). Sedimentation equilibrium analyses revealed that the three PYY analogs were 80-90% monomer at the concentrations used for the subsequent circular dichroism (CD) and H-1-nuclear magnetic resonance (NMR) studies. CD analysis measured helicities for PYY-(1-36), [Pro(34)]PYY, and PYY-(3-36) of 42%, 31%, and 24%, suggesting distinct differences in secondary structure. The backbone H-1-NMR resonances of the three peptides further substantiated marked conformational differences. These patterns support the hypothesis that Y-1 and Y-2 receptor subtype binding affinities depend on the secondary and tertiary solution state structures of PYY and its analogs.