Human AP0BEC3G (A3G ) mutates the HIV genome by deaminafing cDNA cytosines to uracils. This activity can inactivate HIV. However, as a counter-defense, HIV uses an auxiliary protein called Vif (virion infectivity factor) to degrade A3G. A direct protein-protein interaction is required for Vif to neutralize A3G. Although, high-resolution structures of the deaminase domain of A3G have been achieved recently (including two NMR structures from Matsuo laboratory), structures of the full-length A3G protein and its complexes with DNA or Vif have proven more elusive. APOBEC3F (A3F) is another potent HIV-1 restriction factor. Much less structural information is available for A3F as there is no high-resolution structure for this protein. Structural and biochemical studies of A3G and A3F have been hinderd by their insolubility. We have recently generated A3G and A3F variants that are folded, catalytically acitive and soluble enough to take NMR spectra. We propose to solve structures of full-length A3G, the catalytic domain of A3F and their complexes with Vif (or Vif fragments) using NMR. We will also interrogate the interactions between A3G/F and single-stranded DNA. Our objectives are to reveal structurally (1) intra- and inter-molecular domain-domain interaction of A3G and A3F, (2) their mechanisms for binding ssDNA and (S) similarities and differences between A3G and A3F in their Vif-binding domains. These studies are an integral part of a larger interdisciplinary program project that will generate unprecedented molecular, biochemical, biophysical and structural information on this critical host-pathogen interaction.
Structural information of the HIV-1 restriction factors A3G and A3F will provide a strong foundation for further biochemical and cellular studies. In addition, an atomic-level understanding of the A3-Vif interaction can be used to rationally develop new therapeutic methods for HIV/AIDS.
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