Primary structure and conformational analysis of peptide methionine—tyrosine, a peptide related to neuropeptide Y and peptide YY isolated from lamprey intestine

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Abstract
A peptide belonging to the pancreatic‐polypeptide‐fold family of regulatory peptides has been isolated from the intestine of an Agnathan, the sea lamprey (Petromyzon marinus). The primary structure of the peptide (termed peptide methionine – tyrosine) was established as Met‐Pro‐Pro‐Lys‐Pro‐Asp‐Asn‐Pro‐Ser‐Pro10‐Asp‐Ala‐Ser‐Pro‐Glu‐Glu‐Leu‐Ser‐Lys‐Tyr20‐Met‐Leu‐Ala‐Val‐Arg‐Asn‐Tyr‐Ile‐Asn‐Leu30‐Ile‐Thr‐Arg‐Gln‐Arg‐Tyr CONH2. This sequence shows stronger structural similarity with pig neuropeptide Y (64%), particularly in the COOH‐terminal region, than with pig peptide tyrosine – tyrosine (61%) or with pig pancreatic polypeptide (42%). Molecular modelling and dynamic simulation, based upon sequence similarity with turkey pancreatic polypeptide, indicates that the conformations of the polyproline‐helix‐like region (residues 1–8) and the α‐helical region (residues 15–30) in turkey pancreatic polypeptide are conserved in peptide methionine – tyrosine, and that non‐bonded interactions between these domains have preserved the overall polypeptide fold in the molecule. The substitution of the otherwise totally conserved Gly9 residue by serine in lamprey peptide methionine – tyrosine, however, results in a preferred structure in which the conformation of the β‐turn between the two helical domains (residues 9–14) is appreciably different.