An immunochemical study of avian pancreatic polypeptide: the nature of the principal epitope.
Structural features contributing to the antigenic recognition of the small globular hormone avian pancreatic polypeptide (APP) by a polyclonal antiserum have been defined using a solution phase radioimmunoassay technique. Cross-reactivity studies with PP homologues suggest that the surface residues within the alpha-helix of the peptide may be antigenic, whereas hydrophilicity and atomic mobility predictive methods implicate the molecules beta-turn region. Immunochemical data and circular dichroism measurements on a timed trypsin digest of APP indicate that the secondary structure of the alpha-helix is vital for the molecule's immunological competence. Immunoreactivities of iodinated derivatives of APP, as well as that of peptide fragments of APP and its homologues, support the importance of teritary structure involving the interaction of the polyproline and alpha helices. The highly mobile C-terminal residues 34-36 (His-Arg-Tyr-NH2) have been found by immunological analysis to be unimportant. Arginine residue 33, which has been conserved through vertebrate evolution, is a major antigenic contributor, since a large decrease in immunoreactivity, not accompanied by a significant change in conformation, was observed upon specific removal of this residue by carboxypeptidase B. These results are consistent with a "discontinuous" epitopic model for APP in which Arg-33 and exposed residues in the alpha-helix are principal components of an epitope or epitopes mediated by the secondary and tertiary structures of the molecule.
Taylor
T C
TC
Department of Biochemistry, University of Kansas Medical Center, Kansas City 66103.
Thompson
D O
DO
Ebner
K E
KE
Kimmel
J R
JR
Rawitch
A B
AB
D000818:Animals; D002268:Carboxypeptidases; D055598:Chemical Phenomena; D002621:Chemistry; D003429:Cross Reactions; D000939:Epitopes / Q000032:analysis*; D007455:Iodine; D010191:Pancreatic Polypeptide / Q000276:immunology*; D010446:Peptide Fragments / Q000276:immunology; D010455:Peptides / Q000276:immunology; D011863:Radioimmunoassay; D014357:Trypsin
D000939:Epitopes; D010446:Peptide Fragments; D010455:Peptides; C009725:pancreatic polypeptide, avian; D010191:Pancreatic Polypeptide; D007455:Iodine; D002268:Carboxypeptidases; D014357:Trypsin