CBFβ was recently found to be a key regulator of the ability of human immunodeficiency virus type 1 (HIV-1) Vif to overcome host antiviral APOBEC3 proteins. However, the detailed molecular requirements for the Vif-CBFβ interaction are still not clear. Here, we mapped the minimum Vif domain required for CBFβ binding. In terms of CBFβ binding, the Vif N terminus was very sensitive to deletions. We determined that the Vif fragment from residues 5 to 126 was sufficient to form a stable complex with CBFβ in vitro. We also observed that ionic interactions were not the main contributor to the interaction between Vif and CBFβ. Instead, hydrophobic interactions were important for maintaining the Vif-CBFβ complex, since it could be disrupted by nonionic detergent. Site-directed mutagenesis of conserved hydrophobic amino acids revealed novel residues in Vif that were important for CBFβ binding and APOBEC3 inactivation. At least part of the well-characterized HCCH domain (residues 108 to 139) was required to form a stable Vif-CBFβ complex. Thus, the HCCH motif may have a dual role in binding both Cul5 and CBFβ. Considering the importance of Vif in HIV-1 infection, this unique Vif-CBFβ interaction represents an attractive pharmacological intervention target against HIV-1.
Importance: Vif-induced APOBEC3 protein degradation was the first host antiviral mechanism against HIV-1/simian immunodeficiency virus to be revealed, yet details regarding which proteins are degraded are not fully demonstrated. Recently, host cellular factor CBFβ was found to be essential for Vif to function and promote viral infectivity. In this study, we present more critical information on the Vif-CBFβ interaction by revealing that hydrophobicity contributes the most to the Vif-CBFβ interaction and locating several novel hydrophobic sites (tryptophans and phenylalanines) that are conserved among Vif proteins from different lentiviruses and essential for Vif binding to CBFβ. Mutations on these sites result in a reduced/abolished Vif-CBFβ interaction, leading to the attenuated potency of Vif on both inducing the degradation of antiviral factors like APOBEC3G and promoting HIV-1 infectivity. Therefore, information from this study will help people to further understand how Vif acts against host antiviral mechanism, which is important for novel anti-HIV-1 drug development.