| Hijack of the ubiquitin proteasome system is a recurring theme in host-pathogen interactions. HIV-1 encodes at least three `accessory factor' proteins, Vif, Vpr, and Vpu, each known to interact with and retarget a human ubiquitin ligase with deleterious consequences for the host. The best characterized of the accessory factors is Vif, which is required for viral infectivity in T-lymphocytes. In the absence of Vif, the APOBEC3 family of restriction factors is expressed in these cells and induces lethal hypermutation of the viral genome. Vif serves as a viral countermeasure to APOBEC3 proteins by recruiting them to CUL5, a member of the CRL ubiquitin ligases, for K48-linked polyubiquitination thereby sentencing them to proteasomal degradation. Affinity purification-mass spectrometry approaches implicate a large cast of cellular proteins as Vif interactors; the work in this dissertation focuses on understanding the functional significance of a small number of them for Vif. In summary, we find the NEDD8 E2 enzyme UBE2F is critical for activation of the Vif-hijacked ubiquitin ligase, and is recruited to CUL5 by the RING-protein RBX2. The NEDD8 pathway is druggable at the E1 step, and the UBE2F pathway represents a novel drug target for relatively specific inhibition of Vif. Ligands influence the conformational state of Vif, a natively disordered protein. We find that Vif is able to simultaneously bind nucleic acids and components of the ubiquitylation machinery, resulting in a conformation with physical properties not observed in Vif complexes lacking either nucleic acid or ubiquitylation components. |
