Core-binding factor β increases the affinity between human Cullin 5 and HIV-1 Vif within an E3 ligase complex

Abstract

HIV-1 Vif masquerades as a receptor for a cellular E3 ligase harboring Elongin B, Elongin C, and Cullin 5 (EloB/C/Cul5) proteins that facilitate degradation of the antiretroviral factor APOBEC3G (A3G). This Vif-mediated activity requires human core-binding factor β (CBFβ) in contrast to cellular substrate receptors. We observed calorimetrically that Cul5 binds tighter to full-length Vif((1-192))/EloB/C/CBFβ (K(d) = 5 ± 2 nM) than to Vif((95-192))/EloB/C (K(d) = 327 ± 40 nM), which cannot bind CBFβ. A comparison of heat capacity changes supports a model in which CBFβ prestabilizes Vif((1-192)) relative to Vif((95-192)), consistent with a stronger interaction of Cul5 with Vif's C-terminal Zn(2+)-binding motif. An additional interface between Cul5 and an N-terminal region of Vif appears to be plausible, which has therapeutic design implications.

Figure 1

Schematic of the Vif-mediated E3 ligase and Vif sequence motifs. (A) A3G is recruited by Vif to the N-terminus of Cullin 5 (herein called Cul5(N)) in conjunction with the heterodimeric EloB/C substrate adaptor. Cul5(C) and Rbx2 position the E2 ubiquitin conjugase. (B) Conserved Vif binding motifs.

Figure 2

Heat capacity change (ΔC_p) for interaction of Cul5(N) with Vif_C/EloB/C and Vif/EloB/C/CBFβ taken as the slope of best-fit lines.