Abstract
Some human APOBEC3 cytidine deaminases have antiviral activity against HIV-1 and other retroviruses. The single deaminase domain APOBEC3H (A3H) enzyme is highly polymorphic and multiple A3H haplotypes have been identified. A3H haplotype II (A3H-hapII) possesses the strongest activity against HIV-1. There remains, however, uncertainty regarding the extent to which A3H-hapII is sensitive to HIV-1 Vif mediated degradation. We tested, therefore, the two different reference Vif proteins widely used in previous studies. We show that A3H-hapII is resistant to NL4-3 Vif while it is efficiently degraded by LAI Vif. Co-immunoprecipitation assays demonstrate that LAI Vif, but not NL4-3 Vif associates with A3H-hapII. Chimeras between NL4-3 and LAI Vif identify the amino acid responsible for the differential degradation activity: A histidine at position 48 in Vif confers activity against A3H-hapII, while an asparagine abolishes its anti-A3H activity. Furthermore, the amino acid identity at position 48 only affects the degradation of A3H-hapII, whereas recognition of and activity against human A3D, A3F and A3G are only minimally affected. NL4-3 encoding 48H replicates better than NL4-3 WT (48N) in T cell-lines stably expressing A3H hapII, whereas there is no fitness difference in the absence of APOBEC3. These studies provide an explanation for the conflicting reports regarding A3H resistance to Vif mediated degradation.
Highlights
The human APOBEC3 family consists of seven deaminase proteins (A3A to A3H) that can restrict HIV-1 in cell culture [1,2]
A3H Sensitivity to NL4-3 and LAI Vif To test whether the difference in Vif sensitivity of A3H-hapII is caused by the different Vif variants, we first determined the efficiency of Vif-mediated A3H-hapII degradation in the producer cell
NL4-3 WT was more sensitive to A3G than LAI WT, suggesting that LAI Vif counteracts A3G more efficiently than NL4-3 Vif. These results show that NL4-3 Vif and LAI Vif expressed from fulllength HIV-1 both counteracted A3G, but only LAI Vif counteracted A3H-hapII
Summary
The human APOBEC3 family consists of seven deaminase proteins (A3A to A3H) that can restrict HIV-1 in cell culture [1,2]. They exert their activity by deaminating single stranded viral cDNA during reverse transcription resulting in numerous G-to-A mutations in the provirus [3,4,5]. APOBEC3H (A3H), one of the single deaminase domain enzymes, was initially found to lack anti-HIV-1 activity due to its low protein stability [8,9,10]. The allelic frequency of the active A3H-hapII is high in African and low in European and Asian populations [11,14]
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