CAEV Vif Hijacks ElonginB/C, CYPA and Cullin5 to Assemble the E3 Ubiquitin Ligase Complex Stepwise to Degrade oaA3Z2-Z3

Abstract

Caprine arthritis encephalitis virus (CAEV) is a lentivirus that causes multisystemic chronic disorders in sheep and goats. It encodes Vif to counteract the restriction of Ovis aries A3Z2-Z3 (oaA3Z2-Z3) by inducing their degradation. Nevertheless, the mechanisms underlying the interplay between CAEV Vif and OaA3Z2-Z3 have yet to be elucidated. Here, we identified the cellular factors ElonginB/C, CYPA and Cullin5 as being hijacked by CAEV Vif as well as several functional domains of CAEV Vif required for degrading oaA3Z2-Z3. Moreover, we determined that CAEV Vif assembled E3 ubiquitin ligase stepwise via its SLE motif (170SLE172) to recruit ElonginB/C, the P21 site and the zinc finger motif (C132-C134-C154-C157) to recruit CYPA, as well as the hydrophobic domain (141IR142) to recruit Cullin5. And this CAEV Vif-mediated E3 ligase triggers the proteasomal degradation of oaA3Z2-Z3, which directly bind CAEV Vif through residues Y39 and L44. In particular, CYPA played an essential role in the process to regulate ligase assembly, which was analogous to CBF-β, the essential regulator for HIV-1 and SIV-mediated E3 ligase, indicating that there is a modular conservation and lineage-specific preference for cellular partners required by Vifs from different subgroups of lentiviruses. Taken together, these findings provide important insights regarding the CAEV Vif function and deepen our understanding of the arms race between the lentiviruses and their hosts.

Maedi–visna virus Vif protein uses motifs distinct from HIV-1 Vif to bind zinc and the cofactor required for A3 degradation

“…1 D ). This result shows that, like the CAEV Vif ( 28 ), the CCCC motif of the MVV Vif is important for cofactor CypA binding and therefore the overall structural integrity and function of the Vif itself.…”

“…1 A ). Likewise, KCCC, CCCC, and HCCC motifs have been proposed to be structurally important for zinc binding in Vif proteins originating from feline immunodeficiency virus (FIV), caprine arthritis encephalitis virus (CAEV), and bovine immunodeficiency virus (BIV), respectively ( 27 , 28 , 29 ) ( Fig. 1 B ).…”

“…Interestingly, while the HCCH motif of HIV-1 Vif is important for Cul5 binding, it is dispensable for interaction with its cellular cofactor CBFβ (13,21,30). In contrast, a recent study showed that the zinc-binding CCCC motif of CAEV Vif was essential for binding its cofactor CypA (28). This difference in the function of the zinc-binding motifs may suggest significant structural differences in the overall fold of HIV-1 Vif compared to MVV Vif.…”

Potential APOBEC-mediated RNA editing of the genomes of SARS-CoV-2 and other coronaviruses and its impact on their longer term evolution

“…Per the current model, Vif recruits an E3 ubiquitin ligase complex composed of Elongin B/C, cullin 5, RING-box subunit 2 (Rbx2), and core-binding factor (CBFβ) to polyubiquitinate A3G, leading to degradation via the host proteasome ( Fribourgh et al, 2014 ; Guo et al, 2014 ; Jäger et al, 2011 ; Zhang et al, 2011 ). Vif-like proteins have been described for other lentiviruses including simian immunodeficiency virus, feline immunodeficiency virus, bovine immunodeficiency virus, jembrana disease virus, visna/maedi virus, and caprine arthritis encephalitis virus ( Kristbjörnsdóttir et al, 2004 ; Nakano et al, 2017 ; Wang et al, 2018 ; Zhang et al, 2014 ; Zhao et al, 2019 ; Zielonka et al, 2010 ). Species-specific spumaretrovirinae, another subfamily of retroviruses, infect a diverse number of mammals and encode the accessory protein Bet, which impairs the activity of A3G through direct binding and sequestration rather than targeted degradation ( Jaguva Vasudevan et al, 2013 ; Löchelt et al, 2005 ; Russell et al, 2005 ).…”

Retroviral Restriction Factors and Their Viral Targets: Restriction Strategies and Evolutionary Adaptations

“…APOBEC3G (A3G) was originally identified as a restriction factor for its ability to inhibit the replication of Vif-deficient HIV-1 [ 124 ]. Both human A3G and its mammalian orthologs also restrict other lentiviruses and other retroviruses [ 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 ]. A3G is packaged into viral particles and, in subsequently infected cells, it can catalyze the deamination reaction on newly formed viral single-stranded DNA during reverse transcription [ 134 , 135 ].…”