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.
Available from: Greg Owens
- "Combinatorial approaches allow the selection of ligands in an unbiased functional assay without preconceptions about the nature of targets in disease (Mintz and others 2003). Phagedisplayed random peptide libraries have successfully identified a rheumatoid factorspecific mimotope (Zhang and Davidson 1999) and have mapped neutralizing antibodies to the Puumala hantavirus (Heiskanen and others 1999), HIV antigens (Ferrer and others 1999), and coronavirus-specific epitopes (Zhong and others 2005). "
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ABSTRACT: Multiple sclerosis (MS) is a chronic demyelinating disorder of unknown etiology, possibly caused by a virus or virus-triggered immunopathology. The virus might reactivate after years of latency and lyse oligodendrocytes, as in progressive multifocal leukoencephalopathy, or initiate immunopathological demyelination, as in animals infected with Theiler's murine encephalomyelitis virus or coronaviruses. The argument for a viral cause of MS is supported by epidemiological analyses and studies of MS in identical twins, indicating that disease is acquired. However, the most important evidence is the presence of bands of oligoclonal IgG (OCBs) in MS brain and CSF that persist throughout the lifetime of the patient. OCBs are found almost exclusively in infectious CNS disorders, and antigenic targets of OCBs represent the agent that causes disease. Here, the authors review past attempts to identify an infectious agent in MS brain cells and discuss the promise of using recombinant antibodies generated from clonally expanded plasma cells in brain and CSF to identify disease-relevant antigens. They show how this strategy has been used successfully to analyze antigen specificity in subacute sclerosing panencephalitis, a chronic encephalitis caused by measles virus, and in neuromyelitis optica, a chronic autoimmune demyelinating disease produced by antibodies directed against the aquaporin-4 water channel.
Available from: ncbi.nlm.nih.gov
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ABSTRACT: We have used phage-displayed peptide libraries to identify novel ligands to the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120. Screening of libraries of random 12-mers, 7-mers, and cyclic 9-mers produced two families of gp120 binding peptides. Members of a family with the prototype sequence RINNIPWSEAMM (peptide 12p1) inhibit the interaction between gp120 and both four-domain soluble CD4 (4dCD4) and monoclonal antibody (MAb) 17b, a neutralizing antibody that covers the chemokine receptor binding surface on gp120. Peptide 12p1 inhibits the interaction of 4dCD4 with gp120 from three different HIV strains, implying that it binds to a conserved site on gp120. Members of a second family of peptides, with the prototype sequence TSPYEDWQTYLM (peptide 12p2), bind more weakly to gp120. They do not detectably affect its interaction with 4dCD4, but they enhance its binding to MAb 17b. A common sequence motif in the two peptide families and cross-competition for gp120 binding suggest that they have overlapping contacts. Their divergent effects on the affinity of gp120 for MAb 17b may indicate that their binding stabilizes distinct conformational states of gp120. The functional properties of 12p1 suggest that it might be a useful lead for the development of inhibitors of HIV entry.
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