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

Abstract

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,

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

“…This result confirms that either N15⌬ or R105G mutation can completely disrupt A3H expression (12,27,46). We next compared levels of A3H protein expression among different haplotypes.…”

“…Recently, Li et al (20) confirmed that A3H hap I is completely resistant to HIV-1 Vif, but they reported that the A3H hap II (NRRDD) protein was partially sensitive to HIV-1 Vif. It was concluded that the increased Vif sensitivity was due to a single K121D mutation in the A3H protein (20,46). However, in the investigation carried out by Harari et al (12), A3H hap II was completely resistant to HIV-1 Vif.…”

“…5). Next, we tried to replicate work showing the K121D mutation could reduce A3H resistance to HIV-1 Vif, as reported by others (20,46). However, we found that both hap II and VII, which have a D121 and K121 residue, respectively, were equally resistant to HIV-1 Vif (Fig.…”

“…5A). Recently, two groups reported that A3H could become partially sensitive to HIV-1 Vif if the K121 residue was changed to an aspartate (K121D) (20,46). We therefore introduced a K121D or K121E mutation into Mut I, creating another two mutants, Mut II and III.…”

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

“…A3H hapI-GKE resists HIV-1 Vif-mediated degradation, whereas A3H hapII-RDD is differentially sensitive to Vif from different HIV-1 strains (20,32). The aspartic acid (D) at position 121 of hapII-RDD was previously identified as the main determinant for resistance to HIV-1 Vif (28,47).…”