Disulfide Sensitivity in the Env Protein Underlies
Lytic Inactivation of HIV‑1 by Peptide Triazole Thiols
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Abstract
We investigated the mode of action
underlying lytic inactivation
of HIV-1 virions by peptide triazole thiol (PTT), in particular the
relationship between gp120 disulfides and the C-terminal cysteine-SH
required for virolysis. Obligate PTT dimer obtained by PTT SH cross-linking
and PTTs with serially truncated linkers between pharmacophore isoleucine–ferrocenyltriazole-proline–tryptophan
and cysteine-SH were synthesized. PTT variants showed loss of lytic
activity but not binding and infection inhibition upon SH blockade.
A disproportionate loss of lysis activity vs binding and infection
inhibition was observed upon linker truncation. Molecular docking
of PTT onto gp120 argued that, with sufficient linker length, the
peptide SH could approach and disrupt several alternative gp120 disulfides.
Inhibition of lysis by gp120 mAb 2G12, which binds at the base of
the V3 loop, as well as disulfide mutational effects, argued that
PTT-induced disruption of the gp120 disulfide cluster at the base
of the V3 loop is an important step in lytic inactivation of HIV-1.
Further, PTT-induced lysis was enhanced after treating virus with
reducing agents dithiothreitol and tris (2-carboxyethyl)phosphine.
Overall, the results are consistent with the view that the binding
of PTT positions the peptide SH group to interfere with conserved
disulfides clustered proximal to the CD4 binding site in gp120, leading
to disulfide exchange in gp120 and possibly gp41, rearrangement of
the Env spike, and ultimately disruption of the viral membrane. The
dependence of lysis activity on thiol–disulfide interaction
may be related to intrinsic disulfide exchange susceptibility in gp120
that has been reported previously to play a role in HIV-1 cell infection