Sole copy of Z2‐type human cytidine deaminase APOBEC3H has inhibitory activity against retrotransposons and HIV‐1.

Several members of the human APOBEC3 family of cytidine deaminases can potently restrict retroviruses such as HIV-1. The single-domain APOBEC3H (A3H) is encoded by four haplotypes, of which only A3H haplotype II-RDD (hapII-RDD) restricts HIV-1 efficiently. The goal of this study was to elucidate the mechanisms underlying the differences in antiviral activity among A3H haplotypes. The naturally occurring A3H hapI-GKE and hapII-RDD variants differ at three amino acid positions. A panel of six site-directed mutants containing combinations of the three variable residues was used to determine A3H protein expression, requirements of A3H virion incorporation, and A3H-Gag interactions. The catalytic activity of each A3H protein was assessed directly by using an Escherichia coli mutator assay. We found that the incorporation efficiencies of A3H variants into HIV-1 virions were comparable despite major differences in cellular expression. An assessment of the enzymes' catalytic activities showed that the deaminase activity of each A3H variant correlated with protein expression, suggesting similar enzymatic efficiencies. Surprisingly, virion incorporation experiments using Gag deletion mutants demonstrated that A3H haplotypes interacted with different Gag regions. A3H hapII-RDD associated with nucleocapsid in an RNA-dependent manner, whereas A3H hapI-GKE associated with the C-terminal part of matrix and the N-terminal capsid domain. Our results show that the A3H hapII-RDD interaction with nucleocapsid is critical for its antiviral activity and that the inability of A3H hapI-GKE to interact with nucleocapsid underlies its limited antiviral potential. Thus, the antiviral activity of A3H haplotypes is determined by its incorporation into the viral core, in proximity to the reverse transcription complex.

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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The Localization of APOBEC3H Variants in HIV-1 Virions Determines Their Antiviral Activity

Ooms

Majdak

Seibert

et al. 2010

“…It is still unclear if there are any other haplotypes in humans, particularly those that can be stably expressed. So far, several groups have observed the anti-HIV-1 activity of human A3H hap I and II (6,12,18,27,39), and two groups found that A3H also inhibits the replication of non-long terminal repeat (LTR) retrotransposons, including long interspersed nuclear element 1 (LINE-1) and the short interspersed nuclear element (SINE) Alu (17,39). However, it is still unclear how A3H is packaged into virions and whether human A3H can be neutralized by HIV-1 Vif.…”

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confidence: 99%

Analysis of Human APOBEC3H Haplotypes and Anti-Human Immunodeficiency Virus Type 1 Activity

Wang

Abudu

Son

et al. 2011

102

188

Human APOBEC3H (A3H) has one cytidine deaminase domain (CDD) and inhibits the replication of retrotransposons and human immunodeficiency virus type 1 (HIV-1) in a Vif-resistant manner. Human A3H has five single amino acid polymorphisms (N15⌬, R18L, G105R, K121D, and E178D), and four haplotypes (I to IV) have previously been identified in various human populations. Haplotype II was primarily found in African-derived populations, and it was the only one that could be stably expressed. Here, we identified three new haplotypes from six human population samples, which we have named V, VI, and VII. Haplotypes V and VII are stably expressed and inhibit HIV-1 replication. Notably, haplotype V was identified in samples from all African-, Asian-, and Caucasian-derived populations studied. Using haplotype VII, we investigated the A3H anti-HIV-1 mechanism. We found that A3H virion packaging is independent of its CDD but dependent on a 112 YYXW 115 motif. This motif binds HIV-1 nucleocapsid in an RNA-dependent manner, and a single Y112A mutation completely disrupts A3H virion incorporation. We further studied the mechanism of A3H resistance to Vif. Although the previously identified APOBEC3G Vif-responsive motif 128 DPDY 131 is not conserved in A3H, placement of this motif into A3H does not make it become less resistant to HIV-1 Vif. We conclude that stably expressed A3H haplotypes may be more broadly distributed in humans than previously realized, and A3H protein is resistant to Vif. These results have important implications for the role of A3H in retrotransposon and HIV-1 inhibition.

“…It encodes a conserved cytidine deaminase and is capable of inducing mutation in prokaryotes (19,29,58,59). A3H mRNA has been detected in several human tissues, including peripheral blood mononuclear cells, and is moderately upregulated in macrophages by interferons (29,58,59,79). When transfected into mammalian cells, it is insufficiently expressed and has weak antiretroviral activity (59).…”

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confidence: 99%

A Single Amino Acid Difference in Human APOBEC3H Variants Determines HIV-1 Vif Sensitivity

Zhen

Wang

Zhao

et al. 2010

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Several variants of APOBEC3H (A3H) have been identified in different human populations. Certain variants of this protein are particularly potent inhibitors of retrotransposons and retroviruses, including HIV-1. However, it is not clear whether HIV-1 Vif can recognize and suppress the antiviral activity of A3H variants, as it does with other APOBEC3 proteins. We now report that A3H_Haplotype II (HapII), a potent inhibitor of HIV-1 in the absence of Vif, can indeed be degraded by HIV-1 Vif. Vif-induced degradation of A3H_HapII was blocked by the proteasome inhibitor MG132 and a Cullin5 (Cul5) dominant negative mutant. In addition, Vif mutants that were incapable of assembly with the host E3 ligase complex factors Cul5, ElonginB, and ElonginC were also defective for A3H_HapII suppression. Although we found that Vif hijacks the same E3 ligase to degrade A3H_HapII as it does to inactivate APOBEC3G (A3G) and APOBEC3F (A3F), more Vif motifs were involved in A3H_HapII inactivation than in either A3G or A3F suppression. In contrast to A3H_HapII, A3H_Haplotype I (HapI), which differs in only three amino acids from A3H_HapII, was resistant to HIV-1 Vif-mediated degradation. We also found that residue 121 was critical for determining A3H sensitivity and binding to HIV-1 Vif.The apolipoprotein B mRNA-editing catalytic polypeptide 3 (APOBEC3) protein family is composed of cytidine deaminases that are capable of editing nucleic acids, converting cytidines to uracils (2,12,15,18,26,27,31,45,82,91). Members of this family of host cell proteins (APOBEC3A, -B, -C, -DE, -F, -G, and -H) have been shown to have differential inhibitory effects on various retroviruses and retroelements that are mediated through cytidine deamination and other mechanisms (4,