THE EFFECTS OF SELECTIVE AMINO-ACID SUBSTITUTION UPON NEUROPEPTIDE-Y ANTISECRETORY POTENCY IN RAT JEJUNUM MUCOSA

The antisecretory potency of NPY and a series of truncated and structural analogues of NPY have been tested upon mucosal preparations of rat small intestine. Single amino acid substitutions, i.e., [Ile34]NPY, [Pro34]NPY, resulted in severe attenuation and loss of biological activity, respectively, and neither peptide affected NPY responses. An agonist order of potency: NPY greater-than-or-equal-to [Glu16,Ser18,Ala22,Leu28,31]NPY (ESALL-NPY) > [Cys2,Aoc5-24,DCys27]NPY (C2-NPY) > [Aoc5-24]NPY > [Des-Ser3,Des-Lys4]C2-NPY >> [Cys5,Aoc7-20,DCys24]NPY (C5-NPY) greater-than-or-equal-to [DCys7,Aoc8-17, Cys20]NPY (C7-NPY) > [Aoc8-17]NPY greater-than-or-equal-to [Ile34]C7-NPY >> [Aoc2-27]NPY >> [Pro34]C2-NPY was obtained. The use of analogues based upon the tertiary structural model of NPY with varying amounts of N- and C-terminal helical regions removed and replaced with a single 8-aminooctanoic acid residue (Aoc) has allowed us to assess the structural requirements for activation of the epithelial Y2 receptor. From the agonist order of potency we infer a critical importance for both N (1-4)- and C (25-36)-terminal regions in close apposition to each other. The polyproline helix, beta-turn and majority of the amphipathic alpha-helix serve a structural role bringing N- and C-terminal residues together for optimal receptor recognition and activation.