A single amino acid of APOBEC3G controls its species-specific interaction with virion infectivity factor (Vif)

Abstract

The virion infectivity factor (Vif) accessory protein of HIV-1 forms a complex with the cellular cytidine deaminase APOBEC3G (apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3G) to block its antiviral activity. The antiviral property of APOBEC3G is conserved in several mammalian species, but the ability of Vif to block this activity is species-specific. HIV-1 Vif blocks human APOBEC3G but does not block the mouse or African green monkey (AGM) enzyme. Conversely, SIVAGM Vif blocks the antiviral activity of AGM but not human APOBEC3G. We demonstrate that the species specificity is caused by a single amino acid difference in APOBEC3G. Replacement of Asp-128 in human APOBEC3G with the Lys-128 of AGM APOBEC3G caused the enzyme to switch its interaction, becoming sensitive to SIVAGM Vif and resistant to HIV-1 Vif. Conversely, the reciprocal Lys to Asp switch in AGM APOBEC3G reversed its specificity for Vif. The reversal of biological activity was accompanied by the corresponding switch in the species specificity with which the enzyme physically associated with Vif and was excluded from virions. The charge of the amino acid at position 128 was a critical determinant of species specificity. Based on the crystal structure of the distantly related Escherichia coli cytidine deaminase, we propose that this amino acid is positioned on a solvent-exposed loop of APOBEC3G on the same face of the protein as the catalytic site.

Restriction of Equine Infectious Anemia Virus by Equine APOBEC3 Cytidine Deaminases

“…It also contributed to explain the narrow host range of HIV-1 that shows spreading replication only in humans and chimpanzees (49,59). Such defined interactions of Vif proteins with cognate A3 proteins had been shown so far only for HIV, SIV, and Feline immunodeficiency virus (49,58,74). But the discovery of the Vif-A3 interaction also highlighted the conundrum of "simple" mammalian retroviruses like Mo-MLV and Mouse mammary tumor virus and their survival without accessory genes like the vif gene (45,(64)(65)(66).…”

HIV-1 Vif-mediated ubiquitination/degradation of APOBEC3G involves four critical lysine residues in its C-terminal domain

“…Abrogation of Vif binding by A3G could also confer resistance to Vif-dependent degradation, as was observed for the D128K mutant (27)(28)(29)(30). It therefore seemed prudent to determine whether Arg substitutions at A3G residues 297, 301, 303, and 334 would in any way interfere with A3G's ability to bind Vif.…”

“…The region in A3G responsible for binding to HIV-1 Vif was initially identified by comparative studies of the species specificity of A3G degradation by Vif. Thus, a single amino acid difference in hA3G, Asp at position 128 versus Lys in the A3G of African green monkeys (A3G agm ), determines species specificity by influencing Vif-A3G binding (27)(28)(29)(30). Furthermore, extensive site-directed mutagenesis revealed that the 128 DPD 130 motif of A3G, located near the first Zn cluster, is crucial for direct binding to HIV-1 Vif.…”

Inhibition of HIV-1 replication by simian restriction factors, TRIM5α and APOBEC3G

“…Recent studies demonstrated that single aminoacid substitutions in the human TRIM5a and human APOBEC3G could render the human proteins potent restriction factors against HIV-1. [33][34][35][36][37] Thus, as suggested by Yap et al, 37 we can use the R332P derivative of human TRIM5a, in combination with the Vif-insensitive, K128D derivative of human APOBEC3G, as ideal alternatives to reduce host immune response to the restriction factors.…”

“…In contrast, HIV-1 Vif cannot neutralize agm-APOBEC3G. 34 We therefore examined the anti-viral effects of agm-APOBEC3G on HIV-1 replication. The HA-tagged agm-APOBEC3G-expressing retroviral vector, pBabe-puroaA3G, was produced by cloning the EcoRI-XhoI fragment of pc-AGM-APOBEC3G-HA into the EcoRI-SalI sites of pBabe-puro.…”