Binding of the 2F5 Monoclonal Antibody to Native and Fusion-Intermediate Forms of Human Immunodeficiency Virus Type 1 gp41: Implications for Fusion-Inducing Conformational Changes

Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Bethesda, Maryland 20892-4555, USA.
Journal of Virology (Impact Factor: 4.44). 04/2004; 78(5):2627-31. DOI: 10.1128/JVI.78.5.2627-2631.2004
Source: PubMed


We investigated how the broadly neutralizing monoclonal antibody 2F5 affects the human immunodeficiency virus type 1 envelope
glycoprotein as it undergoes receptor-induced conformational changes and show that 2F5 binds both native and fusion-intermediate
conformations, suggesting inhibition of a late step in virus entry. We also demonstrate conformational changes in the C heptad
of gp41.

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Available from: Renate Kunert
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    • "The HR1, HR2 and loop domains become available as early as upon CD4 binding and are lost concomitant with the onset of cell-cell fusion. By comparison, the tryptophan-rich membrane-proximal external region (MPER), which is C-terminal to the gp41 HR2 domain, is accessible to the neutralizing antibodies, 2F5 and 4E10, on the native structure, but the MPER accessibility is gradually lost as fusion progresses to the content mixing stage [116,117,125]. The exposure of HR1 and HR2 domains upon interactions with CD4 is also supported by the enhanced binding of C- and N-peptides targeting these domains [117,119,126-128]. "
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    ABSTRACT: Enveloped viruses encode specialized fusion proteins which promote the merger of viral and cell membranes, permitting the cytosolic release of the viral cores. Understanding the molecular details of this process is essential for antiviral strategies. Recent structural studies revealed a stunning diversity of viral fusion proteins in their native state. In spite of this diversity, the post-fusion structures of these proteins share a common trimeric hairpin motif in which the amino- and carboxy-terminal hydrophobic domains are positioned at the same end of a rod-shaped molecule. The converging hairpin motif, along with biochemical and functional data, implies that disparate viral proteins promote membrane merger via a universal "cast-and-fold" mechanism. According to this model, fusion proteins first anchor themselves to the target membrane through their hydrophobic segments and then fold back, bringing the viral and cellular membranes together and forcing their merger. However, the pathways of protein refolding and the mechanism by which this refolding is coupled to membrane rearrangements are still not understood. The availability of specific inhibitors targeting distinct steps of HIV-1 entry permitted the identification of key conformational states of its envelope glycoprotein en route to fusion. These studies provided functional evidence for the direct engagement of the target membrane by HIV-1 envelope glycoprotein prior to fusion and revealed the role of partially folded pre-hairpin conformations in promoting the pore formation.
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    • "In this context, a β-galactosidase sensor displaying an HIV gp41 epitope and responsive to human HIV-immune sera is preferentially activated by the IgG4 antibody subpopulation [51]. As at least in the case of HIV infection the ability of anti-viral antibodies to modify the epitope's conformation is strongly related to their neutralizing activity [52,53] and probably to the progression of the infection [54], allosteric biosensing could eventually offer a valuable instrument for high-throughput sera analysis for prognostic investigation. "
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    ABSTRACT: The quantitative detection of low analyte concentrations in complex samples is becoming an urgent need in biomedical, food and environmental fields. Biosensors, being hybrid devices composed by a biological receptor and a signal transducer, represent valuable alternatives to non biological analytical instruments because of the high specificity of the biomolecular recognition. The vast range of existing protein ligands enable those macromolecules to be used as efficient receptors to cover a diversity of applications. In addition, appropriate protein engineering approaches enable further improvement of the receptor functioning such as enhancing affinity or specificity in the ligand binding. Recently, several protein-only sensors are being developed, in which either both the receptor and signal transducer are parts of the same protein, or that use the whole cell where the protein is produced as transducer. In both cases, as no further chemical coupling is required, the production process is very convenient. However, protein platforms, being rather rigid, restrict the proper signal transduction that necessarily occurs through ligand-induced conformational changes. In this context, insertional protein engineering offers the possibility to develop new devices, efficiently responding to ligand interaction by dramatic conformational changes, in which the specificity and magnitude of the sensing response can be adjusted up to a convenient level for specific analyte species. In this report we will discuss the major engineering approaches taken for the designing of such instruments as well as the relevant examples of resulting protein-only biosensors.
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    • "Understanding how Env interacts with these receptors and, moreover, how presently available monoclonal antibodies (mAbs) inhibit these interactions would be a step toward this goal. Studies to date have revealed that mAb b12 blocks gp120-CD4 binding [2]; mAbs directed to gp120 epitopes that are induced by sCD4, as well as V3 mAbs, interfere with CCR5 binding [43-45]; and 2F5 and 4E10 appear to prevent fusion events that occur after CD4 and CCR5 binding, though they may also bind to Env in its native form [12,46]. In comparison, relatively little is known about how these mAbs might block virus attachment to various cells, and indeed what Env determinants are important (12). "
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