A Highly Conserved Arginine in gp120 Governs HIV-1 Binding to Both Syndecans and CCR5 via Sulfated Motifs

Abstract

HIV-1 has maximized its utilization of syndecans. It uses them as in cis receptors to infect macrophages and as in trans receptors to infect T-lymphocytes. In this study, we investigated at a molecular level the mechanisms that control HIV-1-syndecan interactions. We found that a single conserved arginine (Arg-298) in the V3 region of gp120 governs HIV-1 binding to syndecans. We found that an amine group on the side chain of this residue is necessary for syndecan utilization by HIV-1. Furthermore, we showed that HIV-1 binds syndecans via a 6-O sulfation, demonstrating that this binding is not the result of random interactions between basic residues and negative charges, but the result of specific contacts between gp120 and a well defined sulfation in syndecans. Surprisingly, we found that Arg-298, which mediates HIV-1 binding to syndecans, also mediates HIV-1 binding to CCR5. We postulated that HIV-1 recognizes similar motifs on syndecans and CCR5. Supporting this hypothesis, we obtained several lines of evidence that suggest that the 6-O sulfation recognized by HIV-1 on syndecans mimics the sulfated tyrosines recognized by HIV-1 in the N terminus of CCR5. Our finding that CCR5 and syndecans are exploited by HIV-1 via a single determinant echoes the mechanisms by which chemokines utilize these two disparate receptors and suggests that the gp120/ chemokine mimicry may represent a common strategy in microbial pathogenesis.The dominant cell surface heparan sulfate proteoglycans (HSPGs) 3 are the syndecans. Syndecans are transmembrane receptors highly expressed on adherent cells (i.e. epithelial cells, endothelial cells, and macrophages), but poorly expressed on suspension cells (i.e. T-lymphocytes) (1-4). The syndecan family is composed of four members, syndecan-1 to -4. Their ectodomain bears linear heparan sulfate chains, which are composed of a repetition (30 -400 repeats) of a sulfated disaccharide motif (5). The sulfation pattern of the heparan sulfates dictates the ligand specificity of syndecans. Syndecans via their heparan sulfates function as co-factors in cell-cell adhesion, in linking cells to ligands in the extracellular matrix, and in the binding and activation of cellular growth factors (5). Syndecans also function as receptors for HIV-1. We and others demonstrated that pretreatment of HIV-1 target cells (i.e. CD4ϩ T cell lines, CD4ϩ HeLa cells, and CD4ϩ CHO cells or macrophages) with heparinase, an enzyme that removes heparan sulfates from the ectodomain of syndecans, significantly reduces HIV-1 infectivity (1, 6 -11). Zhang et al. (11), using CHO cells that either express HSPGs (CHO-K1) or lack HSPGs (pgsA745), obtained evidence that HSPGs favor HIV-1 infection in a gp120-dependent manner. Previous work suggests that the requirement for syndecans and HSPGs in HIV-1 infection is particularly accentuated when target cells express low levels of entry receptors (CD4 and CCR5/CXCR4) such as CD4ϩ HeLa cells and macrophages (1). However, why and how HIV-1 uses sulfated syndecans to optimally infect these t...

The HIV-1 Envelope Glycoprotein gp120 Features Four Heparan Sulfate Binding Domains, Including the Co-receptor Binding Site

“…Lys 305 takes part of a typical basic stretch of amino acids, RKRIR (HBD 2; residues 304 -308) at the very beginning of the V3 loop. Interestingly, a few residues upstream of this sequence, Arg 298 was recently found to be involved in HS recognition (45). Finally, Lys 500 defined a third cluster of basic amino acids, KAKRR (HBD 3; residues 500 -504), at the C-terminal domain of the protein.…”

Syndecan-3 is a dendritic cell-specific attachment receptor for HIV-1

“…However, the domains in gp120 required for HIV-1-syndecan and HIV-1-C-type lectins are distinct. An arginine located in the third variable region of gp120 is necessary for HIV-1-syndecan interactions (44), whereas mannose residues on the immunologically silent face of gp120 are necessary for HIV-1-Ctype lectin interactions (45). Recent failures of clinical trials using microbicides to prevent HIV-1 transmission demonstrate the complexity of HIV-1 transmission and indicate that more knowledge is needed to develop an effective microbicide (46).…”

Computer-assisted anti-AIDS drug development: cyclophilin B against the HIV-1 subtype A V3 loop

“…However, the evidence of study [49] demonstrating that increase of immunophilins concentration in infected blood plasma does not influence the virus infectivity conflicts with this primitive conjecture. In the case of Cyc B, the probable cause of its insufficient neutralizing activity may consist in the fact that, as follows from our simulations, the binding of the immunophilin to the HIV-1 V3 loop occurs via interactions with the central region of V3 and does not affect its N-and C-terminals (Figure 1) where the major portion of the residues involved in cell tropism and cell fusion is localized [50][51][52]. Therefore, to amplify the blockade of V3 and preserve its capacity for specific interactions with Cyc B, we have undertaken an attempt to design as potential anti-HIV-1 drug the virtual molecule named Cyc B peptide and imitating N-terminal segment 1-30 of the native immunophilin.…”