The APOBEC3 antiviral factors are single-stranded DNA cytosine deaminases that potently restrict HIV replication by hypermutation of viral cDNA replication intermediates. Several of these enzymes also have the capacity to restrict virus replication by a deaminase-independent mechanism that involves direct binding to viral RNA genomes. HIV counteracts this threat by encoding an accessory protein called Vif, which hijacks cellular CBF? and an E3-ligase complex to bind up to five APOBEC3s and target them for proteasomal degradation (APOBEC3C, APOBEC3D, APOBEC3F, APOBEC3G, and APOBEC3H). Despite considerable progress over the past two decades, a comprehensive biochemical and structural understanding of these APOBEC3-Vif complexes is still lacking. Here, we propose to fill these gaps in knowledge through two specific aims.
In Aim 1 we will determine structures of Vif-CBF?-E3 ubiquitin ligase complexes.
In Aim 2 we will determine the atomic details of multiple A3-Vif complexes using x-ray crystallography and/or single-particle cryo-EM. These structures will demonstrate the mechanisms used by Vif to interact with multiple host factors and protect the virus from APOBEC3-mediated restriction. A detailed biochemical and structural understanding of these host-pathogen interactions is anticipated to inform the development of new antiviral strategies such as therapeutic targeting of conserved structural motifs.
HIV infection and AIDS remain pandemic problems. Determining structures of HIV-1 Vif and APOBEC3-Vif complexes will provide insights into motifs that may inform the development of new antiviral therapies.
