Design and synthesis of a highly immunogenic, discontinuous epitope of HIV-1 gp120 which binds to CD4+ve transfected cells

Here we report the design and synthesis of a novel 32-mer peptide, Lys364-378Val445-459.oxidized (named GC-1), which represents a discontinuous epitope from the C3 and C4 domains of gp120 from the HIV-1 IIIB isolate. This peptide induces high titre IgG antibody responses in mice, indicating that it has both B and T cell epitopes. Epitope mapping using reduced GC-1 and appropriate linear peptides demonstrated that a large proportion of the antibodies raised in mice were directed against discontinuous epitope(s). Furthermore, antibodies to GC-1 peptide cross-reacted with purified HIV-1 strain IIIB gp120, indicating that GC-1 mimicked at least one epitope of the native protein. The peptide, which incorporates three gp120 residues Asp 368, Glu 370 and Asp 457, previously shown to be critical for CD4 ligation, bound to the surface of a CD4 transfected human epithelial cell line HeLa, but not to the parent cell line and inhibited binding of recombinant HIV-1 gp120 to recombinant soluble CD4. We have synthesized the first of a series of discontinuous peptides which will be useful for the probing of interactions of HIV-1 gp 120 with the CD4 molecule.