PEPTIDES WITH CARBOXYL-TERMINAL SEQUENCE OF ALANINE PROLINE - DETECTION BY A HUMAN MONOCLONAL-ANTIBODY

A human B lymphoblastoid cell line JWCI-L94 secretes an IgM human mono clonal antibody (HuMAb) that reacts with human melanoma cell lines, M1 4 and M12. To identify the antigenic epitope of this antibody, we scre ened lambda gt11 expression libraries constructed from M14 and M12. A total of 12 immunoreactive clones were isolated, and their DNA sequenc es were determined. The only sequence shared by all these clones was a lanine-proline (A-P) at the carboxyl (C) terminal. HuMAb L94 reacted n ot only with C-terminal A-P-containing fusion proteins, but also with the synthetic dipeptide A-P. None of the peptides containing A-P inter nally or amino terminally reacted to HuMAb L94. Proline or alanine alo ne had no ability to bind to HuMAb L94. When alanine was replaced by g lycine (G-P) or proline (P-P), the binding activity of these peptides was similar to that of A-P. On the other hand, when alanine was replac ed by serine, valine, leucine, glutamine, lysine, methionine, phenylal anine, or hydroxyl proline, the resulting peptide completely lost the antigenic activity of HuMAb L94. These results demonstrate that HuMAb L94 recognizes C-terminal A-P, G-P, or P-P, and that a human antibody can recognize peptides as small as a two-amino acid residue.