Characterization Of Vif Domains That Mediate Feline Immunodeficiency Virus Antagonism Of APOBEC3-H And APOBEC3-CH Restriction

Feline immunodeficiency virus (FIV) Vif mediates degradation of two anti-lentiviral feline APOBEC3 (fA3) proteins, fA3Z3 and fA3Z2bZ3. HIV-1 Vif targets the restriction factor human APOBEC3G (A3G, hA3Z2g-Z1c) for proteasome degradation to mediate viral evasion. Despite this similarity, FIV and HIV-1 Vif share limited homology. Vif binds hA3Z2g-Z1c through its N-terminal region, while its C-terminal region binds to an E3-ligase complex containing Cullin5 and Elongin B/C. Further, HIV-1 Vif contains critical domains in its C-terminus, including an adjacent BC box, the only shared domain between FIV and HIV-1 Vif, and a non-classical zinc finger (HCCH) domain. Felid lentivirus Vif, however, contains a highly conserved KCCC motif. While both Vifs have evolved to counteract select A3 antiretroviral proteins, the FIV Vif domains necessary to target fA3s for degradation are incompletely understood. To identify these domains, we used the well-characterized HIV-1 Vif domains to show that distinct mutations within the BC box of FIV Vif prevent fA3Z3 and fA3Z2bZ3 degradation and reduce virion infectivity. We also found that mutating any single residue in the KCCC motif blocked fA3 targeting and impaired FIV infectivity and replication. These mutations also failed to disrupt the FIV Vif and Cullin5 interaction. Further, we showed that, in contrast to the HCCH domain in HIV-1 Vif, the KCCC domain of FIV Vif does not bind zinc. However, unlike HIV-1 Vif, FIV Vif (C36 isolate) reduces intracellular levels of co-expressed Cullin5 proteins, a novel finding. Our results reveal important C-terminal residues in FIV Vif and show that the BC box and KCCC regions are critical for fA3 degradation, infectivity, and spreading replication.