APOBEC3G Antagonism by Vif, or When Structure Meets Biological and Evolutionary Studies

Restriction factors serve as innate host defenses against viruses and act as critical barriers to cross-species transmission. In response, viruses have evolved accessory proteins to counteract restriction factors, enabling evasion of innate immune responses. The interplay between primate APOBEC3G (A3G) and lentiviral virion infectivity factor (Vif) exemplifies a molecular arms race between a restriction factor and its viral antagonist. This review integrates evolutionary and functional analyses of this system, showing how genetic signatures of molecular arms races map onto high-resolution cryo-electron microscopy structures. However, A3G's interaction with Vif is not limited to the evolutionary dynamic interface, characterized by rapidly evolving residues under selective pressure, but also involves a conserved interface mediated by RNA binding that positions A3G for antagonism by Vif. These findings propose a model wherein Vif and potentially other viral antagonists target functional complexes using a dual strategy: leveraging both adaptive interfaces subject to evolutionary pressures and conserved interfaces that constrain host escape mechanisms.