CD4-induced interaction of primary HIV-1 gp120 glycoproteins with the chemokine receptor CCR-5

Abstract

For efficient entry into target cells, primary macrophage-tropic and laboratory-adapted human immunodeficiency viruses type 1 (HIV-1) require particular chemokine receptors, CCR-5 and CXCR-4, respectively, as well as the primary receptor CD4 (refs 1-6). Here we show that a complex of gp120, the exterior envelope glycoprotein, of macrophage-tropic primary HIV-1 and soluble CD4 interacts specifically with CCR-5 and inhibits the binding of the natural CCR-5 ligands, macrophage inflammatory protein (MIP)-1alpha and MIP-1beta (refs 7, 8). The apparent affinity of the interaction between gp120 and CCR-5 was dramatically lower in the absence of soluble CD4. Additionally, in the absence of gp120, an interaction between a two-domain CD4 fragment and CCR-5 was observed. A gp120 fragment retaining the CD4-binding site and overlapping epitopes was able to interact with CCR-5 only if the V3 loop, which can specify HIV-1 tropism and chemokine receptor choice, was also present on the molecule. Neutralizing antibodies directed against either CD4-induced or V3 epitopes on gp120 blocked the interaction of gp12O-CD4 complexes with CCR-5. These results suggest that HIV-1 attachment to CD4 creates a high-affinity binding site for CCR-5, leading to membrane fusion and virus entry.

Analysis of proteins copurifying with the cd4/lck complex using one-dimensional polyacrylamide gel electrophoresis and mass spectrometry: comparison with affinity-tag based protein detection and evaluation of different solubilization methods

“…CD4 has multiple functions in T cell activation [9], as an interleukin-16 receptor [16] and in HIV-1 entry [10,11]. We have investigated previously proteins copurifying with CD4 in search for novel binding partners that could play a role in the function of this receptor [7].…”

“…We have reported previously the use of affinity tag-mediated purification of tryptic peptides containing cysteine residues to identify proteins present in an affinity-purification of CD4 [7], a protein involved in T cell activation [9] and HIV entry [10,11]. We were able to identify the components of the CD4 receptor complex CD4 and lck, a tyrosine kinase that has been reported to associate with CD4 [12] functioning in T cell activation.…”

Viral surface glycoproteins, gp120 and gp41, as potential drug targets against HIV-1: Brief overview one quarter of a century past the approval of zidovudine, the first anti-retroviral drug

“…Additional changes in gp120 occur with CD4 binding, including movement of the V1/V2 and V3 loop domains. As a result, CD4 binding not only induces the formation of the bridging sheet, as it likely also enhances exposure of this region and orients it and the V3 loop toward the target cell membrane, where they can engage the viral co-receptor [83,84]. The HIV-1 gp120 envelope protein is an essential component in the multi-tiered viral entry process.…”

The good and evil of complement activation in HIV-1 infection

“…34 The HIV-1-specific nAbs described to date interfere with viral attachment to the cellular receptor CD4, binding to the coreceptor (most commonly CCR5 or CXCR4), or postreceptor engagement in the actual fusion process. [35][36][37][38][39][40][41][42][43][44][45] When a host is infected with a virus, Abs are produced against many epitopes on multiple viral proteins. These Abs consist of a mixture of nAbs and non-nAbs, which can contribute to antiviral immunity in four ways: 34 (i) nAbs directly neutralize free virus particles; (ii) both nAbs and non-nAbs trigger complement-mediated lysis of free virus particles and infected cells via specific Ab-antigen binding events and complement activation; (iii) both nAbs and non-nAbs bind to and coat viruses to mediate opsonization and phagocytosis by macrophages and other cells; and (iv) both nAbs and non-nAbs trigger destruction of viruses by stimulating other immune responses such as Ab-dependent cellular cytotoxicity (ADCC).…”