HIV-1 Vif: HIV's weapon against the cellular defense factor APOBEC3G

The human immunodeficiency virus type 1, HIV-1, has long been known to possess the viral infectivity factor, Vif, which supports productive viral replication in non-permissive cells, such as peripheral blood lymphocytes (PBL). In the last few years, Vif function has been elucidated by the finding that it inactivates a cellular anti-viral factor named APOBEC3G. Tremendous progress has been made since the initial observation, reflected in a large number of publications. APOBEC3G represents a novel innate defense mechanism against retroviral infection. It is expressed in non-permissive cells and possesses cytidine deaminase activity. APOBEC3G is encapsidated into viral particles and is transported into the infected cell, where it facilitates the deamination of the cytosine residues in the first strand cDNA intermediate during early steps of HIV infection. Vif counteracts APOBEC3G by direct binding, which mediates its degradation by the ubiquitin-dependent proteasomal pathway. In this review, we will summarize the current knowledge about the structure and function of both proteins, their interaction with each other and the mechanism of Vif-mediated APOBEC3G inactivation. In addition, we will discuss possible interference strategies as potential new drugs against HIV infection.