Structural and functional characterization of an epitope in the conserved C-terminal region of HIV-1 gp120.
Through an integrated study of the reactivity of a monoclonal antibody, 803-15.6, with synthetic peptides and native recombinant HIV-1 envelope glycoprotein gp120, we have obtained structure-functional information on a region of rgp120 not yet elucidated by X-ray crystallography. mAb 803-15.6 binds with high affinity and broad cross-clade specificity to the conserved C-terminal region (amino acids 502-516) of HIV-1 rgp120. Phage display selection from a random peptide library identified the core binding motif as AXXKXRH, homologous to residues 502-508. Using quantitative binding analyses, the affinity of mAb 803-15.6 for native, monomeric recombinant gp120HXB2 (rgp120) was found to be similar to that for the synthetic gp120 peptide (502-516). Circular dichroism studies indicate that the synthetic peptide largely has a random coil conformation in solution. The results therefore suggest that the 803-15.6 epitope is fully accessible on rgp120 and that this region of rgp120 is as flexible as the synthetic peptide. Residues 502-504 are on the edge of a putative gp41 binding site that has been postulated to change conformation on CD4 binding. However, the affinity of mAb 803-15.6 for rgp120 is not affected by binding of CD4 and vice-versa. These results suggest either that the 502-504 region does not change conformation upon CD4 binding, or that recombinant gp120 does not undergo the same changes as occur in the native viral gp120-gp41 oligomer. The detailed characterization of the 803-15.6 epitope may be useful for further study of the role of the C5 region of gp120 in the viral attachment and fusion process.
Ferrer
M
M
Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA.
Sullivan
B J
BJ
Godbout
K L
KL
Burke
E
E
Stump
H S
HS
Godoy
J
J
Golden
A
A
Profy
A T
AT
van Schravendijk
M R
MR
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015704:CD4 Antigens / Q000378:metabolism; D002942:Circular Dichroism; D017124:Conserved Sequence; D018604:Epitope Mapping; D000939:Epitopes / Q000737:chemistry* / Q000378:metabolism; D005260:Female; D015699:HIV Envelope Protein gp120 / Q000737:chemistry* / Q000378:metabolism; D015497:HIV-1 / Q000737:chemistry*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013329:Structure-Activity Relationship; D020349:Surface Plasmon Resonance
D015704:CD4 Antigens; D000939:Epitopes; D015699:HIV Envelope Protein gp120; D011994:Recombinant Proteins