Binding of the Mannose-Specific Lectin, Griffithsin, to HIV-1 gp120 Exposes the CD4-Binding Site

Abstract

The glycans on HIV-1 gp120 play an important role in shielding neutralization-sensitive epitopes from antibody recognition. They also serve as targets for lectins that bind mannose-rich glycans. In this study, we investigated the interaction of the lectin griffithsin (GRFT) with HIV-1 gp120 and its effects on exposure of the CD4-binding site (CD4bs). We found that GRFT enhanced the binding of HIV-1 to plates coated with anti-CD4bs antibodies b12 and b6 or the CD4 receptor mimetic CD4-IgG2. The average enhancement of b12 or b6 binding was higher for subtype B viruses than for subtype C, while for CD4-IgG2, it was similar for both subtypes, although lower than observed with antibodies. This GRFT-mediated enhancement of HIV-1 binding to b12 was reflected in synergistic neutralization for 2 of the 4 viruses tested. The glycan at position 386, which shields the CD4bs, was involved in both GRFT-mediated enhancement of binding and neutralization synergism between GRFT and b12. Although GRFT enhanced CD4bs exposure, it simultaneously inhibited ligand binding to the coreceptor binding site, suggesting that GRFT-dependent enhancement and neutralization utilize independent mechanisms. This study shows for the first time that GRFT interaction with gp120 exposes the CD4bs through binding the glycan at position 386, which may have implications for how to access this conserved site.

Efficient Single Tobamoviral Vector-Based Bioproduction of Broadly Neutralizing Anti-HIV-1 Monoclonal Antibody VRC01 in Nicotiana benthamiana Plants and Utility of VRC01 in Combination Microbicides

“…Of interest is the fact that VRC01p showed such consistent synergism with other entry inhibitors, suggesting multicomponent entry inhibition as a potential HIV prevention strategy. Presenting results similar to ours, Alexandre et al showed that another CD4bs-specific bnMAb b12 synergized with GRFT in neutralizing infectivity of a few viruses; this was associated with GRFT-mediated enhancement of viral binding to the MAb (62). On the other hand, to our knowledge, this is the first report showing CD4bs-specific bnMAb synergism with CCR5 antagonists and RT inhibitors.…”

Combinations of Griffithsin with Other Carbohydrate-Binding Agents Demonstrate Superior Activity Against HIV Type 1, HIV Type 2, and Selected Carbohydrate-Binding Agent-Resistant HIV Type 1 Strains

“…This allows a more tight interaction of the GRFTbound gp120 with the mAb b12, which may explain the synergistic activity. 39 It could therefore be possible that a similar mechanism of action is responsible for the observed synergy between MVN and the non-CBA mAb b12. Our generated HIV-1 NL4.3…”

UCLA1, a Synthetic Derivative of a gp120 RNA Aptamer, Inhibits Entry of Human Immunodeficiency Virus Type 1 Subtype C

“…Both T20 and b12 have been previously shown to act synergistically with other HIV-1 entry inhibitors (2,37,46,58). Thus, we next evaluated any possible synergistic effects of UCLA1 with T20 or b12.…”

“…The synergy was quantified and expressed as a combination index (CI) using the IC 50 s (8). Calculation of the CI was based on the Chou-Talalay equation: CI ϭ (D) 1 /(Dx) 1 ϩ (D) 2 /(Dx) 2 , in which (Dx) 1 and (Dx) 2 in the denominators are the concentrations of agent 1 and agent 2 alone that are required to neutralize the HIV-1 subtype C Env pseudovirus, and D 1 and D 2 in the numerators are the concentrations of agent 1 and agent 2 when used in combination that also neutralize the virus. A CI value of less than 1, equal to 1, or more than 1, indicates synergism, an additive effect, and antagonism, respectively (8,59).…”

“…The DRI was calculated using the Chou-Talalay equation: that is, DRI 1 and DRI 2 are the first and second terms of the CI equation, respectively. Therefore, DRI 1 ϭ (Dx) 1 /(D) 1 and DRI 2 ϭ (Dx) 2 / (D) 2 (8,37,59).…”