Fab-based Inhibitors Reveal Ubiquitin Independent Functions for HIV Vif Neutralization of APOBEC3 Restriction Factors

Binning JM, et al., 14(1):e1006830, PLoS Pathog., 2018

The HIV protein Viral Infectivity Factor (Vif) antagonize host APOBEC3 (A3) innate immune proteins and contributes to persistent HIV infection. According to previous studies, Vif targets host proteolysis pathways to degrade A3 restriction factors. Current study reports a degradation-independent mechanism of Vif-mediated A3 neutralization by using antibody antigen-binding fragment (Fab) based inhibitors. Fabs were generated against the A3 substrate receptor termed VCBC. VCBC complex is composed of HIV-1 Vif, the transcription co-factor CBFβ, and adapter proteins ELONGIN B and C. Kinetics of various Fabs binding to VCBC complex was studied by Bio-Layer Interferometry (BLI). A Pall ForteBio Octet RED384 instrument equipped with Streptavidin (SA) Biosensor probes were used to perform all BLI assays. Biotinylated VCBC complex was immobilized onto SA sensor tips followed by dipping them in wells containing different concentrations of Fab samples. BLI data obtained were analyzed by using 1:1 binding model. Equilibrium dissociation constants (KD) were determined for all binding interactions studied. Overall findings of this investigation highlight the potential of Fabs as functional probes and suggest that Vif functions via multiple mechanisms to suppress A3 innate immunity.

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