The human APOBEC3G (A3G) DNA cytosine deaminase restricts and hypermutates DNA-based parasites including HIV-1. The viral infectivity factor (Vif) prevents restriction by triggering A3G degradation. Although the structure of the A3G catalytic domain is known, the structure of the N-terminal Vif-binding domain has proven more elusive. Here, we used evolution- and structure-guided mutagenesis to solubilize the Vif-binding domain of A3G, thus permitting structural determination by NMR spectroscopy. A smaller zinc-coordinating pocket and altered helical packing distinguish the structure from previous catalytic-domain structures and help to explain the reported inactivity of this domain. This soluble A3G N-terminal domain is bound by Vif; this enabled mutagenesis and biochemical experiments, which identified a unique Vif-interacting surface formed by the α1-β1, β2-α2 and β4-α4 loops. This structure sheds new light on the Vif-A3G interaction and provides critical information for future drug development.
Bibliographical noteFunding Information:
This work was supported by grants from the US National Institutes of Health (AI073167 to H.M. and GM091743 to R.S.H.). Salary support for T.K. was provided in part by a Toyobo Biotechnology Foundation Fellowship. The University of Minnesota Supercomputing and NMR center (US National Science Foundation, BIR-961477) provided NMR instrumentation. We thank C. Kojima (Institute for Protein Research, Osaka University) for the pCold vector, K. Strebel (US National Institutes of Health) for the pcDNA-hVif plasmid, M. Katahira for advice on structure calculations, Y. Iwatani for advice on degradation assays, Y. Xia for advice on NMR experiments, Y. Hong for supporting preparation of expression vectors, F. Liu for advice on human-cell experiments and K. Walters for editing the manuscript.
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