Core binding factor beta plays a critical role by facilitating the assembly of the Vif-cullin 5 E3 ubiquitin ligase.

ABSTRACT

UNLABELLED The HIV-1 virion infectivity factor (Vif) targets the cellular cytidine deaminases APOBEC3G (A3G) and APOBEC3F (A3F) for degradation via the host ubiquitin-proteasome pathway. Vif recruits a cellular E3 ubiquitin ligase to polyubiquitinate A3G/F. The activity of Vif critically depends on the cellular core binding factor beta (CBFß). In this study, we investigated the Vif-CBFß interaction and the role of CBFß in the E3 ligase assembly. Vif-CBFß interaction requires an extensive region of Vif spanning most of its amino terminus and zinc finger region, and cullin 5 (Cul5) binding enhances the stability of the Vif-CBFß interaction. Our results further demonstrate that CBFß plays a critical role in facilitating Cul5 binding to the Vif/elongin B/elongin C complex. Vif, with or without bound substrate, is unable to bind Cul5 in the absence of CBFß. These studies support the notion that CBFß serves as a molecular chaperone to facilitate Vif-E3 ligase assembly. IMPORTANCE The host antiviral restriction factors A3G/F inhibit viral replication. The HIV-1 protein Vif targets A3G/F for degradation. This immune evasion activity of Vif is dependent on the cellular factor CBFß. Multiple regions of Vif are known to be important for Vif function, but the mechanisms are unclear. The studies described here provide important information about the Vif-CBFß interaction interface and the function of CBFß in E3 ligase assembly. In particular, our comprehensive Vif-CBFß interface mapping results help to delineate the role of various Vif regions, determining if they are important for binding CBFß or A3G/F. Furthermore, our studies reveal an important potential mechanism of CBFß that has not been shown before. Our results suggest that CBFß may serve as a molecular chaperone to enable Vif to adopt an appropriate conformation for interaction with the Cul5-based E3 ligase. This study advances our understanding of how CBFß facilitates the Vif-mediated degradation of APOBEC3 proteins.