Multiple extracellular domains of CCR-5 contribute to human immunodeficiency virus type 1 entry and fusion

Abstract

Human immunodeficiency virus type 1 (HIV-1) entry is governed by the interaction of the viral envelope glycoprotein (Env) with its receptor. The HIV-1 receptor is composed of two molecules, the CD4 binding receptor and a coreceptor. The seven-membrane-spanning chemokine receptor CCR-5 is one of the coreceptors used by primary isolates of HIV-1. We demonstrate that the mouse homolog of CCR-5 (mCCR-5) does not function as an HIV-1 coreceptor. A set of chimeras of human CCR-5 and mCCR-5 was studied for Env-induced cell fusion and HIV-1 infection. Using the HIV-1 ADA envelope glycoprotein in a syncytium formation assay, we show that replacement of any fragment containing extracellular domains of mCCR-5 by its human counterparts is sufficient to allow Env-induced fusion. Conversely, replacement of any fragment containing human extracellular domains by its murine counterpart did not lead to coreceptor function loss. These results show that several domains of CCR-5 participate in coreceptor function. In addition, using a panel of primary nonsyncytium-inducing and syncytium-inducing isolates that use CCR-5 or both CXCR-4 and CCR-5 as coreceptors, we show that the latter dual-tropic isolates are less tolerant to changes in CCR-5 than strains with a more restricted coreceptor use. Thus, different strains are likely to have different ways of interacting with the CCR-5 coreceptor.

Polymorphisms in the CCR5 genes of African green monkeys and mice implicate specific amino acids in infections by simian and human immunodeficiency viruses

“…We believe that the results of our analyses of human/NIH/ Swiss mouse CCR5 chimeras are fully compatible with related evidence from other laboratories which have also implicated the amino terminus and extracellular loops 1 and 2 of human CCR5 in infections by macrophage-tropic HIV-1 (4,8,34,38). However, as discussed elsewhere (8,34), the earlier studies did not give identical results, presumably because the reference proteins, viruses, cell lines, assay methods, and chimera splice sites were distinct. For example, several of these studies used syncytium rather than infection assays, epitope-tagged rather than native CCR5s, or coreceptor overexpression in COS-7 cells.…”

“…Studies of these CCR5 clones suggested that SIV mac251 interacts differently than all tested macrophage-tropic HIV-1 isolates with position 14 in the amino terminus of CCR5, with position 93 in extracellular loop 1, and with extracellular loop 2. Our chimera results differ in several respects from those of other studies (4,8,34,38), in part because the NIH/Swiss mouse CCR5 contains a unique amino acid substitution in extracellular loop 2 that is nonpermissive for HIV-1 infections. We have identified amino acids in three extracellular regions of CCR5 that appear to be critical for HIV-1 coreceptor function.…”

“…It is not known whether coreceptors serve as attachment sites to strengthen virus adhesion or whether their roles are more complex, nor is it known whether CCR5 polymorphisms occur in nonhuman primates such as African green monkeys (AGMs) (Cercopithecus aethiops) that appear to have been infected with immunodeficiency viruses since ancient times (2,7,24,25,28,32). Recent studies of CCR5 chimeras have suggested that multiple extracellular regions contribute to infections by macrophage-tropic isolates of HIV-1 and that no single region is essential (4,8,34,38). If correct, this would imply that mutations of single amino acids in CCR5 would not block coreceptor activity unless they prevented processing to cell surfaces or caused global changes in folding.…”

The broad anti-viral agent glycyrrhizin directly modulates the fluidity of plasma membrane and HIV-1 envelope

“…Because minimal changes in membrane fluidity are logarithmically responsible for infectivity [15], it is plausible that a reduction of fluidity by GL is the primary mechanism causing inhibition of viral infectivity. It has been proposed that membrane and envelope fluidities play a pivotal role in the formation of the wide fusion pore of enveloped viruses, by clustering a substantial number of activated viral fusion proteins derived from multiple ligand-receptor complexes [39][40][41][42][43]. In this respect, GL mainly acts against enveloped viruses.…”

Co‐receptor use by HIV and inhibition of HIV infection by chemokine receptor ligands

“…This has led to the hypothesis that dual tropism may arise by acquisition of the ability to use ECL1 and 2 of CXCR4, while retaining the ability to use the CCR5 N-terminus (61). We and others have noted that R5X4 strains are more sensitive to disruption of CCR5 structure than R5 strains (64,65). In addition, a number of R5X4 HIV-1 strains are markedly more sensitive than R5 strains to RANTES inhibition on cell lines expressing CCR5 (Fig.…”