Abstract
The HIV-1 viral infectivity factor (Vif) is a small basic protein essential for viral fitness and pathogenicity. Some "non-permissive" cell lines cannot sustain replication of Vif(-) HIV-1 virions. In these cells, Vif counteracts the natural antiretroviral activity of the DNA-editing enzymes APOBEC3G/3F. Moreover, Vif is packaged into viral particles through a strong interaction with genomic RNA in viral nucleoprotein complexes. To gain insights into determinants of this binding process, we performed the first characterization of Vif/nucleic acid interactions using Vif intrinsic fluorescence. We determined the affinity of Vif for RNA fragments corresponding to various regions of the HIV-1 genome. Our results demonstrated preferential and moderately cooperative binding for RNAs corresponding to the 5'-untranslated region of HIV-1 (5'-untranslated region) and gag (cooperativity parameter omega approximately 65-80, and K(d) = 45-55 nM). In addition, fluorescence spectroscopy allowed us to point out the TAR apical loop and a short region in gag as primary strong affinity binding sites (K(d) = 9.5-14 nM). Interestingly, beside its RNA binding properties, the Vif protein can also bind the corresponding DNA oligonucleotides and their complementary counterparts with an affinity similar to the one observed for the RNA sequences, while other DNA sequences displayed reduced affinity. Taken together, our results suggest that Vif binding to RNA and DNA offers several non-exclusive ways to counteract APOBEC3G/3F factors, in addition to the well documented Vif-induced degradation by the proteasome and to the Vif-mediated repression of translation of these antiviral factors.
Highlights
The human immunodeficiency virus type 1 (HIV-1) viral infectivity factor (Vif) is a small basic protein essential for viral fitness and pathogenicity
To gain insight into the molecular mechanisms by which Vif regulates HIV-1 replication and counteracts APOBEC3G/3F antiviral activity, we studied Vif binding to HIV-1 RNA and DNA fragments by fluorescence spectroscopy, using the natural fluorescence of the highly conserved Trp residues contained in the Vif N-terminal region [25] to detect the protein/nucleic acid interactions
HIV-1 Vif protein is required for efficient assembly, maturation, core stabilization and early steps of reverse transcription of virions produced by “non-permissive” cells [24, 42,43,44] expressing APOBEC3G/3F, two cytidine deaminase nucleic acid editing enzymes [3, 45]
Summary
Some “non-permissive” cell lines cannot sustain replication of Vif(؊) HIV-1 virions In these cells, Vif counteracts the natural antiretroviral activity of the DNA-editing enzymes APOBEC3G/3F. Vif binds the viral RNA in the cytoplasm of infected cells, forming a 40S mRNP complex that most likely mediates viral RNA interactions with HIV-1 Pr55Gag [23]. To gain insight into the molecular mechanisms by which Vif regulates HIV-1 replication and counteracts APOBEC3G/3F antiviral activity, we studied Vif binding to HIV-1 RNA and DNA fragments by fluorescence spectroscopy, using the natural fluorescence of the highly conserved Trp residues contained in the Vif N-terminal region [25] to detect the protein/nucleic acid interactions.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
