| Description |
Upon infecting a host, viruses immediately face restriction by the host immune system, including innate and adaptive responses. To mediate efficient replication, viruses have evolved a number of mechanisms to subvert and bypass the host immune responses. Among the earliest immune protections encountered by viruses are a group of cellintrinsic immunity proteins called "restriction factors." Restriction factors have been identified that, if not counteracted, are capable of inhibiting viral replication throughout the viral life cycle. One of the primary mechanisms utilized to counteract these restrictions is the manipulation of the cellular ubiquitin ligase system to induce the directed and specific degradation of these cellular factors. In the case of primate lentiviruses (HIVs and SIVs), four proteins (Vif, Vpu, Vpr, and Vpx) have been shown to alter the specificity of this cellular degradation machinery to target restriction factors. In this study, we explore the molecular interaction between the paralogous proteins Vpr (encoded by all primate lentiviruses) and Vpx (encoded by HIV-2 and some SIVs), the cellular ubiquitin ligase composed of Cul4-Roc1-DDB1- DCAF1 and the restriction factors they target for degradation (Mus81 in the case of Vpr and SAMHD1 in the case of Vpx). Through mutation of DCAF1, the substrate specificity factor for the ubiquitin ligase complex, to which Vpr and Vpx are known to directly interact, we show that although they share a high degree of homology, Vpr and Vpx interact with DCAF1 differently. In addition, through the generation of chimeric Vpriv Vpx proteins, we explore the molecular determinants of Vpr and Vpx substrate specificity. To this end, we demonstrate that manipulation of Cul4-DCAF1 substrate specificity by Vpr and Vpx is mediated by nonlinear determinants within the respective proteins, in contrast to previously proposed models. Finally, we demonstrate that Vpr induces the degradation of Mus81 in a manner independent of the induction of G2 arrest, in contrast to recent reports. |
