AEGiS-07IAC: Quantitative analysis of the binding kinetics and thermodynamics of gp120-CD4 interaction reveals a three step process and a new mode of allosteric inhibition of gp120 binding.

7th International AIDS Conference

Florence, Italy — June 16-21, 1991

Quantitative analysis of the binding kinetics and thermodynamics of gp120-CD4 interaction reveals a three step process and a new mode of allosteric inhibition of gp120 binding.

Int Conf AIDS 1991 Jun 16-21; 7:24 (abstract no. M.A.10)
Repke H, Shin J, Haseltine WA; Division of Human Retrovirology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, USA

OBJECTIVE: To understand the conformational pertubations of CD4 and gp120 during the binding process and to find alternative ways of inhibiting binding, syncytia formation and infectivity.

METHODS: gp120 (HIV-1 and HIV-2), soluble and membrane bound CD4/CD4-mutants and immunoadhesins were used to study association/dissociation kinetics, saturation/displacement kinetics and thermodynamics of binding. Selective internalization of CD4 and CD4 mutants was triggered by changing the biophysical properties in the outer leaflet of the membrane via fusion with glycolipid vesicles.

RESULTS: The first step of gp120-CD4 interaction is followed by an energy-dependent process resulting in a high affinity binding (KD = 2.6e-10M). This step is affected by the proper glycosylation of gp120. A subsequent slow isomerization of the complex leads to an almost irreversible binding (KD: 1.2e-11 M) and involves gp120 binding to an additional site at CD4 which has been identified by fusion proteins and mutagenesis. Using a series of truncations and mutants of CD4, we examined a new mechanism of CD4 self aggregation resulting in complete and selective endocytosis. Surprisingly, a series of peptide derivatives which are supposed to mimic one of the extracellular sites of CD4 involved in this interaction, proved to alter the conformation of the primary binding site of the gp 120-CD4 interaction (step 1 and 2). They bind to CD4 and act as allosteric inhibitors of gp120 binding, syncytia formation and infectivity.

CONCLUSIONS: The CD4-gp120 (HIV-1 and HIV-2) interaction is a three step "induced fit" process resulting in a much higher affinity than previously assumed and alters the conformations of both gp120 and CD4. Under certain circumstances, CD4 can aggregate by virtue of interactions in the V1 region. CD4 has a new allosteric binding site. There are ligands interacting with this site which inhibit gp120 binding, syncytia formation and infectivity in the uM range.

Keywords: AEGIS, Antigens, CD4, Kinetics, HIV-1, Drug Interactions, Thermodynamics, Membrane Fusion, Binding Sites, HIV-2, Giant Cells, Anti-HIV Agents, pharmacokinetics, analysis, ICA7
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