Structural Insight into the Human Immunodeficiency Virus Vif SOCS Box and Its Role in Human E3 Ubiquitin Ligase Assembly

Abstract

Human immunodeficiency virus (HIV) virion infectivity factor (Vif) causes the proteasome-mediated destruction of human antiviral protein APOBEC3G by tethering it to a cellular E3 ubiquitin ligase composed of ElonginB, ElonginC, Cullin5, and Rbx2. It has been proposed that HIV Vif hijacks the E3 ligase through two regions within its C-terminal domain: a BC box region that interacts with ElonginC and a novel zinc finger motif that interacts with Cullin5. We have determined the crystal structure of the HIV Vif BC box in complex with human ElonginB and ElonginC. This complex presents direct structural evidence of the recruitment of a human ubiquitin ligase by a viral BC box protein that mimics the conserved interactions of cellular ubiquitin ligases. We further mutated conserved hydrophobic residues in a region downstream of the Vif BC box. These mutations demonstrate that this region, the Vif Cullin box, composes a third E3-ligase recruiting site critical for interaction between Vif and Cullin5. Furthermore, our homology modeling reveals that the Vif Cullin box and zinc finger motif may be positioned adjacent to the N terminus of Cullin5 for interaction with loop regions in the first cullin repeat of Cullin5.

Determinants of Efficient Degradation of APOBEC3 Restriction Factors by HIV-1 Vif

“…Vif acts as a substrate receptor for a Cullin5-Ring E3 (Cul5-E3) ubiquitin ligase complex, which can induce polyubiquitination (poly-Ub) and degradation of A3 enzymes (8,9). This process is mediated by Vif binding to host Cullin5 and the elongin B/C heterodimer (EloB/C) through specific motifs in Vif that mimic human SOCS2 (10)(11)(12)(13)(14). Vif also binds with the transcription cofactor CBF␤ for thermodynamic stability (15,16).…”

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

“…HIV-1 Vif, serving as the substrate receptor, facilitates ubiquitination of A3G by simultaneously binding to the Cul5-EloB/ EloC-Rbx-E2 complex, thereby mimicking the function of cellular suppressor of cytokine signaling (SOCS) box proteins (9,(19)(20)(21). The SOCS box-like motif of Vif is highly conserved among primate lentiviruses and contains a BC box, as well as a Cullin box.…”

N-Terminal Hemagglutinin Tag Renders Lysine-Deficient APOBEC3G Resistant to HIV-1 Vif-Induced Degradation by Reduced Polyubiquitination

“…Several models have been proposed to explain how HIV-1 Vif overcomes the antiviral function of A3G, but the dominant one according to current knowledge illustrates that HIV-1 Vif interacts with A3G to induce its proteasomal degradation (16,43,48,52,62,65,76). During this process, HIV-1 Vif mediates the formation of the Cullin 5-Vif-A3G ubiquitin E3 ligase complex, which marks A3G for proteasomal degradation (34,45,51,64,76,77). The H-X(5)-C-X(17-18)-C-X(3-5)-H (45,53,72,73) and LPX4L (64) motifs in the C-terminal region of Vif bind to Cullin 5, while another C-terminal SLQ(Y/F)LA domain interacts with Elongin B and Elongin C (51,76,77), which help to recruit Vif into the Cullin 5-ubiquitin E3 ligase complex.…”