Antigenic sites on mouse 2.5S nerve growth factor

Immunological determinants of nerve growth factor involved in p140trk (Trk) receptor binding

Monoclonal anti-NGF antibodies that specifically inhibit the biological activity of mouse beta-NGF were used to study the structural determinants involved in the interaction of NGF with its receptors gp75LNGFR and Trk. None of the three antibodies--N60, M15, and 27/21--showed any reactivity toward denatured NGF. Three experimental methods--radioimmunoassay (RIA), enzyme-linked immunoassay (ELISA), and slot blots--detected no significant cross reactivity between the antibodies and BDNF or NT-3. RIA showed that M15 and N60 recognize the same or an overlapping antigenic site, but 27/21 recognizes a different epitope. Only 27/21, and not N60 or M15, immunoprecipitated beta-NGF crosslinked to LNGFR receptor. Thus, the epitope recognized by 27/21 does not overlap the LNGFR receptor binding site. N60, M15, and 27/21 all block binding of NGF to Trk in a manner consistent with competitive inhibition. Purified Fab fragments of N60 and M15 gave similar results to the intact antibodies. The other subunits present in the 7S complex of NGF, i.e. the alpha and gamma subunits, competitively inhibited binding of antibodies to beta-NGF. Only the gamma subunit inhibited phosphorylation of Trk and biological activity of beta-NGF. These findings suggest that the M15, N60, and 27/21 antibodies bind to a specific site on the surface of NGF where they competitively inhibit binding to the Trk NGF receptor. The region encompassing the N-terminus, the C-terminus, and the loop on the surface of beta-NGF containing residues 60-80 is proposed as important for binding to the Trk receptor.

Synthesis of chimeric mouse nerve growth factor precursor and human beta-nerve growth factor in Escherichia coli: immunological properties

The complete mouse prepro-nerve growth factor (NGF) DNA was fused to the carboxyl terminus of the beta-galactosidase (lac-z) gene of Escherichia coli. Similarly, a genomic fragment encoding the human NGF comprising codons 11 to 106 (from a total of 118) was fused to the fifth codon of the amino terminus of beta-galactosidase. Both bacterial vectors produce high amounts of the chimeric proteins. After cell lysis most of the chimeric mouse preproNGF protein is insoluble and appears in the pellet, whereas the majority of the chimeric human beta-NGF remains in the supernatant. Purification of the fusion proteins from the soluble fraction was achieved by affinity chromatography to p-aminophenyl beta-D-thio-galactoside Sepharose. Yields of the purified chimeric proteins were increased threefold to fourfold by the addition of protease inhibitors in the lysis and chromatography buffers. Their antigenic similarity to the preproNGF and mouse beta-NGF was examined by their interaction to sera raised against synthetic peptides which reproduce sequences of the precursor protein and to sera directed against native and denatured mouse beta-NGF using enzyme-linked immunoabsorbent assay (ELISA) techniques. Antibodies to the peptide N2 (-163 to -139) interacted with high affinity with the chimeric mouse preproNGF protein. Antisera to native and denatured mouse beta-NGF interacted with both chimeric proteins but with a variable degree of affinity. These results provide direct evidence that certain antisera to mouse beta-NGF can cross-react with the human beta-NGF molecule.