Crystal Structure of a Soluble APOBEC3G Variant Suggests ssDNA to Bind in a Channel that Extends between the Two Domains

UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology; Schiffer Lab

Publication Date


Document Type



Biochemistry | Enzymes and Coenzymes | Medicinal Chemistry and Pharmaceutics | Medicinal-Pharmaceutical Chemistry | Molecular Biology | Structural Biology | Virology | Viruses


APOBEC3G (A3G) is a single-stranded DNA (ssDNA) cytosine deaminase that can restrict HIV-1 infection by mutating the viral genome. A3G consists of a non-catalytic N-terminal domain (NTD) and a catalytic C-terminal domain (CTD) connected by a short linker. While the CTD catalyzes cytosine deamination, the NTD is believed to provide additional affinity for ssDNA. Structures of both A3G domains have been solved individually; however, a full-length A3G structure has been challenging. Recently, crystal structures of full-length rhesus macaque A3G variants were solved which suggested dimerization mechanisms and RNA binding surfaces, whereas the dimerization appeared to compromise catalytic activity. We determined the crystal structure of a soluble variant of human A3G (sA3G) at 2.5 A and from these data generated a model structure of wild-type A3G. This model demonstrated that the NTD was rotated 90 degrees relative to the CTD along the major axis of the molecule, an orientation that forms a positively charged channel connected to the CTD catalytic site, consisting of NTD loop-1 and CTD loop-3. Structure-based mutations, in vitro deamination and DNA binding assays, and HIV-1 restriction assays identify R24, located in the NTD loop-1, as essential to a critical interaction with ssDNA. Furthermore, sA3G was shown to bind a deoxy-cytidine dinucleotide near the catalytic Zn(2+), yet not in the catalytic position, where the interactions between deoxy-cytidines and CTD loop-1 and loop-7 residues were different from those formed with substrate. These new interactions suggest a mechanism explaining why A3G exhibits a 3' to 5' directional preference in processive deamination.


APOBEC3G, HIV-1 restriction, co-crystal structure, cytosine deaminase, ssDNA binding

DOI of Published Version



Maiti A, Myint W, Delviks-Frankenberry KA, Hou S, Kanai T, Balachandran V, Sierra Rodriguez C, Tripathi R, Kurt Yilmaz N, Pathak VK, Schiffer CA, Matsuo H. Crystal Structure of a Soluble APOBEC3G Variant Suggests ssDNA to Bind in a Channel that Extends between the Two Domains. J Mol Biol. 2020 Nov 20;432(23):6042-6060. doi: 10.1016/j.jmb.2020.10.020. Epub 2020 Oct 22. PMID: 33098858; PMCID: PMC7771068. Link to article on publisher's site

Journal/Book/Conference Title

Journal of molecular biology

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