Antiviral function of APOBEC3G can be dissociated from cytidine deaminase activity.
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.
Newman
Edmund N C
EN
Department of Infectious Diseases, Guy's, King's, and St. Thomas' School of Medicine, King's College London, London SE1 9RT, United Kingdom.
Holmes
Rebecca K
RK
Craig
Heather M
HM
Klein
Kevin C
KC
Lingappa
Jaisri R
JR
Malim
Michael H
MH
Sheehy
Ann M
AM
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
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