title: Antiviral function of APOBEC3G can be dissociated from cytidine deaminase activity.
abstract: The antiretroviral activity of the cellular enzyme APOBEC3G has been attributed to the excessive deamination of cytidine (C) to uridine (U) in minus strand reverse transcripts, a process resulting in guanosine (G) to adenosine (A) hypermutation of plus strand DNAs. The HIV-1 Vif protein counteracts APOBEC3G by inducing proteasomal degradation and exclusion from virions through recruitment of a cullin5 ECS E3 ubiquitin ligase complex. APOBEC3G belongs to the APOBEC protein family, members of which possess consensus (H/C)-(A/V)-E-(X)24-30-P-C-(X)2-C cytidine deaminase motifs. Earlier analyses of APOBEC-1 have defined specific residues that are important for zinc coordination, proton transfer, and, therefore, catalysis within this motif. Because APOBEC3G contains two such motifs, we used site-directed mutagenesis of conserved residues to assess each region's contribution to anti-HIV-1 activity. Surprisingly, whereas either the N- or C-terminal domain could confer antiviral function in tissue culture-based infectivity assays, only an intact C-terminal motif was essential for DNA mutator activity. These findings reveal the nonequivalency of APOBEC3G's N- and C-terminal domains and imply that APOBEC3G-mediated DNA editing may not always be necessary for antiviral activity. Accordingly, we propose that APOBEC3G can achieve an anti-HIV-1 effect through an undescribed mechanism that is distinct from cytidine deamination.
authors.affiliation: Department of Infectious Diseases, Guy's, King's, and St. Thomas' School of Medicine, King's College London, London SE1 9RT, United Kingdom.
authors.forename: Edmund N C
authors.initials: EN
authors.lastname: Newman
authors.forename: Rebecca K
authors.initials: RK
authors.lastname: Holmes
authors.forename: Heather M
authors.initials: HM
authors.lastname: Craig
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Klein
authors.forename: Jaisri R
authors.initials: JR
authors.lastname: Lingappa
authors.forename: Michael H
authors.initials: MH
authors.lastname: Malim
authors.forename: Ann M
authors.initials: AM
authors.lastname: Sheehy
mesh_terms: D000071480:APOBEC-3G Deaminase; D020816:Amino Acid Motifs; D000998:Antiviral Agents / Q000502:physiology*; D002478:Cells, Cultured; D003564:Cytidine Deaminase / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D016346:Gene Products, vif / Q000378:metabolism*; D015497:HIV-1; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics / Q000502:physiology*; D009700:Nucleoside Deaminases; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000502:physiology*; D012097:Repressor Proteins; D014771:Virion / Q000378:metabolism; D054320:vif Gene Products, Human Immunodeficiency Virus
chemical_list: D000998:Antiviral Agents; D016346:Gene Products, vif; D011506:Proteins; D012097:Repressor Proteins; D054320:vif Gene Products, Human Immunodeficiency Virus; D009700:Nucleoside Deaminases; D000071480:APOBEC-3G Deaminase; C464924:APOBEC3G protein, human; D003564:Cytidine Deaminase