Epitope structures recognised by antibodies against the major coat protein(g8p) of filamentous bacteriophage fd (Inoviridae)

To map the accessible surface of filamentous bacteriophage fd particles, th e epitope structures of polyclonal rabbit serum and three mouse monoclonal antibodies raised against complete phage were analysed. Western blot analys is confirmed the major coat protein, gene VIII product (g8p or pVIII), to b e the antigen. Overlapping peptides were synthesised by spot synthesis on c ellulose membranes, covering the whole sequence of g8p. Each of the three t ested monoclonal antibodies, B62-FE2, B62-GF3/G12 and B62-EA11, reacted wit h a core epitope covering ten amino acid residues at or near the amino term inus of g8p. The epitope recognised by B62-FE2 consists of the ten N-termin al amino acid residues of g8p. Extension of the amino terminus by various s equences did not inhibit binding, indicating that a terminal amino group is not essential for the interaction. Both B62-GF3/G12 and B62-EA11 recognise internal epitopes covering amino acid residues 3 to 12 of g8p. The epitope s of the polyclonal rabbit serum were also confined to the 12 N-terminal am ino acid residues. The contribution of individual amino acid residues to th e binding was analysed by a set of peptides containing individual amino aci ds exchanged by glycine. Accessible residues were Glu2, Asp4, Asp5, Pro6, L ys8, Phe11 and Asp12. The positions of the essential amino acid residues wi thin the epitope are in accordance with a helical conformation of the amino -terminal region of g8p. Further, the results suggest new designs of phage display screening vectors to improve their performance in analysing non-lin ear epitopes. (C) 1999 Academic Press.