Function analysis of sequences in human APOBEC3G involved in Vif-mediated degradation

Human APOBEC3G (hA3G) has been identified as an anti-HIV cellular factor. As a counter measure, the HIV-1 protein Vif causes the degradation of hA3G by binding to it and directing it to the cellular proteasome. In this work, we have used hA3G deletion mutants to map the region in hA3G required for its degradation by Vif to hA3G amino acids 105-245, the linker region between the two zinc coordination motifs. A small fragment of hA3G containing only amino acids 105-245 will undergo Vif-induced degradation. However, while amino acids 105-156 of hA3G are required for Vif interaction with hA3G, they are not themselves sufficient for hA3G degradation, a process that further requires amino acids 157-245. While expression of hA3G fragments 1-156 or 157-384 (but not 246-384) can dominantly inhibit the Vif-mediated degradation of full-length hA3G, only the N-terminal fragment inhibits the Vif/hA3G interaction. Inhibition of hA3G degradation by the C-terminal hA3G fragment 157-384 appears to be related to its ability to prevent the polyubiquitination of hA3G induced by Vif, a process that is required for Vif-mediated proteosomal degradation of hA3G. Non-permissive cells stably expressing hA3G 1-156 or hA3G 157-384 are able to inhibit the replication of wild-type HIV-1, thereby verifying the inhibitory effect of these fragments upon Vif-mediated hA3G degradation and suggesting their potential in anti-HIV-1 therapy.