The HIV-neutralizing monoclonal antibody 4E10 recognizes N-terminal sequences on the native antigen

Characterization of the epitope recognized by the broadly neutralizing anti-HIV Ab 4E10 has, heretofore, focused on a linear sequence from the gp4l pretransmembrane region (PTMR). Attempts to generate neutralizing Abs based on this linear epitope sequence have been unsuccessful. We have characterized the antigenic determinants on recombinant glycosylated full-length Ags, and nonglycosylated and truncated Ags recognized by 4E10 using epitope extraction and excision assays in conjunction with MALDI mass spectrometry. The mAb recognized the peptides (34)LWVTVYYGVPVWK(46) and (512)AVGIGAVFLGFLGAAGST MGAASMTLTVQAR(542) located at the N-terminal region of gp120 and gp4l, respectively. Immunoassays verified AV(L/M)FL GFLGAA as the gp4l epitope core. Recognition of the peptide from the gp4l PTMR was detected only in constructs in which the N termini of the mature envelope proteins were missing. In this region, the epitope core is located in the sequence (672)WFDIT NWLWY(681). We hypothesize that the hydrophobic surface of the paratope functions as a "trap" for the viral sequences, which are responsible for insertion into the host cell membrane. As the N-terminal region of gp120, the fusogenic peptide of gp41, and the PTMR of gp4l show high sequence homology among various HIV strains, this model is consistent with the, broadly neutralizing capabilities of 4E10.