Selective Interactions of Polyanions with Basic Surfaces on Human Immunodeficiency Virus Type 1 gp120

Abstract

It is well established that the gp120 V3 loop of T-cell-line-adapted human immunodeficiency virus type 1 (HIV-1) binds both cell-associated and soluble polyanions. Virus infectivity is increased by interactions between HIV-1 and heparan sulfate proteoglycans on some cell types, and soluble polyanions such as heparin and dextran sulfate neutralize HIV-1 in vitro. However, the analysis of gp120-polyanion interactions has been limited to T-cell-line-adapted, CXCR4-using virus and virus-derived gp120, and the polyanion binding ability of gp120 regions other than the V3 loop has not been addressed. Here we demonstrate by monoclonal-antibody inhibition, labeled heparin binding, and surface plasmon resonance studies that a second site, most probably corresponding to the newly defined, highly conserved coreceptor binding region on gp120, forms part of the polyanion binding surface. Consistent with the binding of polyanions to the coreceptor binding surface, dextran sulfate interfered with the gp120-CXCR4 association while having no detectable effect on the gp120-CD4 interaction. The interaction between polyanions and X4 or R5X4 gp120 was readily detectable, whereas weak or undetectable binding was observed with R5 gp120. Analysis of mutated forms of X4 gp120 demonstrated that the V3 loop is the major determinant for polyanion binding whereas other regions, including the V1/V2 loop structure and the NH 2 and COOH termini, exert a more subtle influence. A molecular model of the electrostatic potential of the conserved coreceptor binding region confirmed that it is basic but that the overall charge on this surface is dominated by the V3 loop. These results demonstrate a selective interaction of gp120 with polyanions and suggest that the conserved coreceptor binding surface may present a novel and conserved target for therapeutic intervention.

CXCR4-Tropic HIV-1 Envelope Glycoprotein Functions as a Viral Chemokine in Unstimulated Primary CD4+ T Lymphocytes

“…Another source of viral glycoprotein consists in soluble gp120 secreted by infected cells. Because X4 gp120 has the capacity to bind heparan sulfates, secreted gp120 may form gradients at the surface of the extracellular matrix like chemokines do (60). Thus, recirculating T cells that contact productively infected cells will be exposed locally to several concentrated sources of viral glycoprotein, deriving from gp120 expressed at the cell membrane, bound to heparan sulfates, and incorporated at the surface of neighboring virions.…”

HIV-1–cellular interactions analyzed by single virus tracing

“…In our initial live-cell imaging studies using these VLPs, we had observed different types of particle behavior: free diffusion, brief touches with the plasma membrane, as well as a significant percentage of particles that displayed a rapid, presumably non-productive, immobilization at the plasma membrane in an apparently heparan sulfate dependent manner (Lampe et al 2007). Heparan sulfate has been reported to be involved in HIV-1 cell attachment and to be of functional importance in some types of host cells, but the overall role of heparan sulfate for HIV-1 infection is not entirely clear (Bobardt et al 2003;Moulard et al 2000;Parren et al 1998;Ugolini et al 1999;Zhang et al 2002). In the continuative study presented here, we had made use of the strengths of SVT to investigate the interactions of HIV-1 occurring at the plasma membrane in a quantitative manner.…”

Conformation-Dependent Recognition of HIV gp120 by Designed Ankyrin Repeat Proteins Provides Access to Novel HIV Entry Inhibitors

“…Heparin is usually added during panning to prevent nonspecific RNA binding to the protein or surfaces. Since gp120 has been reported to have multiple heparin binding sites (39) and in vitro efficiently interacts with heparin (40), addition of heparin during the selection process could block otherwise accessible sites on gp120. Indeed, we found that addition of heparin completely obliterated gp120-specific DARPin selection (data not shown).…”