Capture of an early fusion-active conformation of HIV-1 gp41

Abstract

Using an inhibitory synthetic peptide (DP-178) from HIV-1 gp41, we have trapped HIV-1 envelope glycoprotein (Env) undergoing conformational changes during virus entry. Our data show that DP-178 binds gp41 and inhibits Env-mediated membrane fusion after gp120 interacts with cellular receptors, indicating that conformational changes involving the coiled coil domain of gp41 are required for entry. Capture of this fusion-active conformation of Env provides insights into the early events leading to Env-mediated membrane fusion.

Small-molecule inhibitors of HIV-1 entry block receptor-induced conformational changes in the viral envelope glycoproteins

“…It has been hypothesized that, for enveloped viruses such as HIV-1 that fuse viral and target cell membranes at neutral pH, receptor binding by the exterior envelope glycoprotein serves as the trigger that activates the fusogenic functions of the transmembrane envelope glycoprotein (3-6). Indeed, sCD4 binding to the HIV-1 envelope glycoproteins has been reported to result in the exposure of gp41 elements (18)(19)(20). However, as noted above, sCD4 binding can also induce gp120 shedding (16), allowing gp41 exposure by a process not obviously related to virus entry.…”

“…That peptides mimicking the HR2 region inhibit HIV-1 infection in a dominant-negative fashion (17) suggests that, in some relevant conformation of gp41, the HR1 and HR2 regions are not associated. The HR2 region peptides and some gp41-directed monoclonal antibodies bind the HIV-1 envelope glycoproteins better after treatment with soluble CD4 (18)(19)(20)(21), but it is uncertain whether this increase in binding results from an entry-related conformational change, gp120 shedding, or another process.…”

A human monoclonal antibody neutralizes diverse HIV-1 isolates by binding a critical gp41 epitope

“…Beads were mixed in the presence or absence of competitors, incubated overnight at room temperature, and analyzed on a Fusion ␣-FP HT instrument (Perkin-Elmer), as suggested by the manufacturer. Six-helical bundle formation was measured by using the peptide C34-HA (22). Serial dilutions of inhibitors (D5-IgG1, C34, C34AAA, and 2F5) were preincubated with biotinylated 5H (final concentration, 10 nM) for 40 min at room temperature, then C34-HA was added to a final concentration of 3.3 nM along with AlphaScreen beads for detection of HA-tagged proteins (Amersham Pharmacia) and read on the Fusion instrument.…”

C-terminal Octylation Rescues an Inactive T20 Mutant

“…The analogy between the structural organizations of gp41 and hemagglutinin, the fusion protein of influenza virus (16), and the inhibitory activity of gp41 Cpeptides lead to postulate a "pre-hairpin intermediate" in gp41-induced membrane fusion in which the N-terminal coiled coil is formed but the C-terminal helices are not packed (10,13). At this stage, the C-peptide inhibitors can bind to the exposed coiled coil, thus preventing the subsequent refolding and blocking fusion (12). In addition, extensive biophysical studies done with constructs corresponding to part of SIV gp41 ectodomain suggested that gp41 monomers, which might be present in equilibrium with the trimers, could be also a possible target for C-peptides binding and subsequent inhibition (40).…”

“…The three-dimensional structures of a protease-resistant core of HIV-1 gp41 (9, 10) as well as a segment of SIV gp41 ectodomain that lacks the fusion peptide (11) show that three N-terminal heptad repeats fold into a trimeric coiled coil, against which three antiparallel helices formed by C-terminal heptad repeats are packed. This structure is thought to form at a late stage during the membrane fusion process (12).…”