Generation of a replication-competent simian–human immunodeficiency virus, the neutralization sensitivity of which can be enhanced in the presence of a small-molecule CD4 mimic

et al. 2017

J Virol

Human immunodeficiency virus type 1 (HIV-1) entry into cells is mediated by the viral envelope glycoproteins (Env), a trimer of three gp120 exterior glycoproteins, and three gp41 transmembrane glycoproteins. The metastable Env is triggered to undergo entry-related conformational changes when gp120 binds sequentially to the receptors, CD4 and CCR5, on the target cell. Small-molecule CD4-mimetic compounds (CD4mc) bind gp120 and act as competitive inhibitors of gp120-CD4 engagement. Some CD4mc have been shown to trigger Env prematurely, initially activating Env function, followed by rapid and irreversible inactivation. Here, we study CD4mc with a wide range of anti-HIV-1 potencies and demonstrate that all tested CD4mc are capable of activating as well as inactivating Env function. Biphasic dose-response curves indicated that the occupancy of the protomers in the Env trimer governs viral activation versus inactivation. One CD4mc bound per Env trimer activated HIV-1 infection. Envs with two CD4mc bound were activated for infection of CD4-negative, CCR5-positive cells, but the infection of CD4-positive, CCR5-positive cells was inhibited. Virus was inactivated when all three Env protomers were occupied by the CD4mc, and gp120 shedding from the Env trimer was increased in the presence of some CD4mc. Env reactivity and the on rates of CD4mc binding to the Env trimer were found to be important determinants of the potency of activation and entry inhibition. Cross-sensitization of Env protomers that do not bind the CD4mc to neutralization by an anti-V3 antibody was not evident. These insights into the mechanism of antiviral activity of CD4mc should assist efforts to optimize their potency and utility.IMPORTANCE The trimeric envelope glycoproteins of human immunodeficiency virus type 1 (HIV-1) mediate virus entry into host cells. Binding to the host cell receptors, CD4 and CCR5, triggers changes in the conformation of the HIV-1 envelope glycoprotein trimer important for virus entry. Small-molecule CD4-mimetic compounds inhibit HIV-1 infection by multiple mechanisms: (i) direct blockade of the interaction between the gp120 exterior envelope glycoprotein and CD4; (ii) premature triggering of conformational changes in the envelope glycoproteins, leading to irreversible inactivation; and (iii) exposure of cryptic epitopes to antibodies, allowing virus neutralization. The consequences of the binding of the CD4-mimetic compound to the HIV-1 envelope glycoproteins depends upon how many of the three subunits of the trimer are bound and upon the propensity of the envelope glycoproteins to undergo conformational changes. Understanding the mechanistic factors that influence

Section: Discussionmentioning

confidence: 36%

Section: Resultsmentioning

confidence: 99%

Activation and Inactivation of Primary Human Immunodeficiency Virus Envelope Glycoprotein Trimers by CD4-Mimetic Compounds

Madani

Princiotto

et al. 2017

J Virol

“…The above observations suggest that MF275 binds the Env trimer of some HIV-1 strains in its pretriggered (state 1) conformation and induces changes that promote virus entry into CD4-negative cells expressing CCR5. The binding of CD4-mimetic compounds also produces similar activating events in Env (33,34,54) and further sensitizes primary HIV-1 to inhibition by antibodies that are otherwise ineffective at neutralizing the virus (59)(60)(61)(62)(63). To test whether MF275 might also sensitize HIV-1 to antibody neutralization, HIV-1 AD8 , HIV-1 YU2 , and HIV-1 JR-FL were incubated with mixtures of MF275 and various antibodies directed against HIV-1 Env.…”

Section: Resultsmentioning

confidence: 99%

Strain-Dependent Activation and Inhibition of Human Immunodeficiency Virus Entry by a Specific PF-68742 Stereoisomer

Princiotto

Nguyen

et al. 2019

J Virol

Human immunodeficiency virus (HIV-1) entry into cells is mediated by the viral envelope glycoprotein (Env) trimer, which consists of three gp120 exterior glycoproteins and three gp41 transmembrane glycoproteins. When gp120 binds sequentially to the receptors CD4 and CCR5 on the target cell, the metastable Env trimer is triggered to undergo entry-related conformational changes. PF-68742 is a small molecule that inhibits the infection of a subset of HIV-1 strains by interfering with an Env function other than receptor binding. Determinants of HIV-1 resistance to PF-68742 map to the disulfide loop and fusion peptide of gp41. Of the four possible PF-68742 stereoisomers, only one, MF275, inhibited the infection of CD4-positive CCR5-positive cells by some HIV-1 strains. MF275 inhibition of these HIV-1 strains occurred after CD4 binding but before the formation of the gp41 six-helix bundle. Unexpectedly, MF275 activated the infection of CD4-negative CCR5-positive cells by several HIV-1 strains resistant to the inhibitory effects of the compound in CD4-positive target cells. In contrast to CD4 complementation by CD4-mimetic compounds, activation of CD4-independent infection by MF275 did not depend upon the availability of the gp120 Phe 43 cavity. Sensitivity to inhibitors indicates that MF275-activated virus entry requires formation/exposure of the gp41 heptad repeat (HR1) as well as CCR5 binding. MF275 apparently activates a virus entry pathway parallel to that triggered by CD4 and CD4-mimetic compounds. Strain-dependent divergence in Env conformational transitions allows different outcomes, inhibition or activation, in response to MF275. Understanding the mechanisms of MF275 activity should assist efforts to optimize its utility. IMPORTANCE Envelope glycoprotein (Env) spikes on the surface of human immunodeficiency virus (HIV-1) bind target cell receptors, triggering changes in the shape of Env. We studied a small molecule, MF275, that also induced shape changes in Env. The consequences of MF275 interaction with Env depended on the HIV-1 strain, with infection by some viruses inhibited and infection by other viruses enhanced. These studies reveal the strain-dependent diversity of HIV-1 Envs as they undergo shape changes in proceeding down the entry pathway. Appreciation of this diversity will assist attempts to develop broadly active inhibitors of HIV-1 entry.

“…Common epitopes include the CD4-induced (CD4i) or CoRBS and V3 epitopes ( 100 , 101 , 109 ). While nNAbs poorly neutralize Envs that predominantly occupy State 1 ( 50 , 77 , 80 , 82 , 88 ), they are able to potently neutralize Envs favoring States 2 and 3 ( 43 , 44 , 50 , 53 , 66 – 70 , 87 , 90 , 107 , 110 , 120 – 126 ) ( Fig. 1 ).…”

Section: Env Conformational Statesmentioning

confidence: 99%

The HIV Env Glycoprotein Conformational States on Cells and Viruses

Swartz

et al. 2022

mBio