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Amino-terminal region of the human immunodeficiency virus type 1 nucleocapsid is required for human APOBEC3G packaging.

ABSTRACT: APOBEC3G exerts its antiviral activity by targeting to retroviral particles and inducing viral DNA hypermutations in the absence of Vif. However, the mechanism by which APOBEC3G is packaged into virions remains unclear. We now report that viral genomic RNA enhances but is not essential for human APOBEC3G packaging into human immunodeficiency virus type 1 (HIV-1) virions. Packaging of APOBEC3G was also detected in HIV-1 Gag virus-like particles (VLP) that lacked all the viral genomic RNA packaging signals. Human APOBEC3G could be packaged efficiently into a divergent subtype HIV-1, as well as simian immunodeficiency virus, strain mac, and murine leukemia virus Gag VLP. Cosedimentation of human APOBEC3G and intracellular Gag complexes was detected by equilibrium density and velocity sucrose gradient analysis. Interaction between human APOBEC3G and HIV-1 Gag was also detected by coimmunoprecipitation experiments. This interaction did not require p6, p1, or the C-terminal region of NCp7. However, the N-terminal region, especially the first 11 amino acids, of HIV-1 NCp7 was critical for HIV-1 Gag and APOBEC3G interaction and virion packaging. The linker region flanked by the two active sites of human APOBEC3G was also important for efficient packaging into HIV-1 Gag VLP. Association of human APOBEC3G with RNA-containing intracellular complexes was observed. These results suggest that the N-terminal region of HIV-1 NC, which is critical for binding to RNA and mediating Gag-Gag oligomerization, plays an important role in APOBEC3G binding and virion packaging.

SUBMITTER: Luo K

PROVIDER: S-EPMC523292 | biostudies-other | 2004 Nov

REPOSITORIES: biostudies-other

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Project description:BACKGROUND:The native pre-fusion structure of gp120/gp41 complex of human immunodeficiency virus type 1 was recently revealed. In the model, the helices of gp41 (?6, ?7, ?8, and ?9) form a four-helix collar underneath trimeric gp120. Gp41 is a class I fusion protein and mediates membrane fusion by forming a post-fusion structure called the six-helix bundle (6HB). The comparison of the pre- and post-fusion structures revealed the large conformational changes in gp41 during the antiparallel packing of the N- and C-terminal heptad repeats (NHRs and CHRs) in membrane fusion. Several mutagenesis studies of gp41 performed in the past were interpreted based on 6HB, the only available structure at that time. To obtain an insight about the current pre-fusion structural model and conformational changes during membrane fusion, alanine insertion mutagenesis of the NHR, CHR and connecting loop regions of HXB2 gp41 was performed. The effects of mutations on biosynthesis and membrane fusion were analyzed by immunoblotting and fusion assays, respectively. The extent of membrane fusion was evaluated by split luciferase-based pore formation and syncytia formation assays, respectively. RESULTS:Consistent with the current structural model, drastic negative effects of mutations on biosynthesis and membrane fusion were observed for NHR, loop, and proximal regions of CHR (up to amino acid position 643). The insertions in ?9 after it leaves the four-helix collar were tolerable for biosynthesis. These CHR mutants showed varying effects on membrane fusion. Insertion at position 644 or 645 resulted in poor pore and syncytia formation. Efficient pore and syncytia formation almost similar to that of the wild type was observed for insertion at position 647, 648 or 649. However, recovery of virus infectivity was only observed for the insertions beyond position 648. CONCLUSIONS:The mutagenesis data for HXB2 gp41 is in agreement with the recent pre-fusion structure model. The virus infection data suggested that fusion pores sufficiently large enough for the release of the virus genome complex are formed after the completion of 6HB beyond position 648.

Project description:BackgroundAmong persons living with human immunodeficiency virus (PHIV), incident heart failure (HF) rates are increased and outcomes are worse; however, the role of amino-terminal pro-B-type natriuretic peptide (NT-proBNP) concentrations among PHIV with HF has not been characterized.MethodsPatients were derived from a registry of those hospitalized with HF at an academic center in a calender year. We compared the NT-proBNP concentrations and the changes in NT-proBNP levels between PHIV with HF and uninfected controls with HF.ResultsAmong 2578 patients with HF, there were 434 PHIV; 90% were prescribed antiretroviral therapy and 62% were virally suppressed. As compared to controls, PHIV had higher admission (3822 [IQR, 2413-7784] pg/ml vs 5546 [IQR, 3257-8792] pg/ml, respectively; P < .001), higher discharge (1922 [IQR, 1045-4652] pg/ml vs 3372 [IQR, 1553-5452] pg/ml, respectively; P < .001), and lower admission-to-discharge changes in NT-proBNP levels (32 vs 48%, respectively; P = .007). Similar findings were noted after stratifying based on left ventricular ejection fraction (LVEF). In a multivariate analysis, cocaine use, a lower LVEF, a higher NYHA class, a higher viral load (VL), and a lower CD4 count were associated with higher NT-proBNP concentrations. In follow-up, among PHIV, a higher admission NT-proBNP concentration was associated with increased cardiovascular mortality (first tertile, 11.5; second tertile, 20; third tertile, 44%; P < .001). Among PHIV, each doubling of NT-proBNP was associated with a 19% increased risk of death. However, among patients living without HIV, each doubling was associated with a 27% increased risk; this difference was attenuated among PHIV with lower VLs and higher CD4 counts.ConclusionsPHIV with HF had higher admission and discharge NT-proBNP levels, and less change in NT-proBNP concentrations. Among PHIV, VLs and CD4 counts were associated with NT-proBNP concentrations; in follow-up, higher NT-proBNP levels among PHIV were associated with cardiovascular mortality.

Project description:Several members of the APOBEC3 DNA cytosine deaminase family can potently inhibit Vif-deficient human immunodeficiency virus type 1 (HIV-1) by catalyzing cytosine deamination in viral cDNA and impeding reverse transcription. HIV-1 counteracts restriction with the virally encoded Vif protein, which targets relevant APOBEC3 proteins for proteasomal degradation. HIV-1 Vif is optimized for degrading the restrictive human APOBEC3 repertoire, and, in general, lentiviral Vif proteins specifically target the restricting APOBEC3 enzymes of each host species. However, simian immunodeficiency virus SIVmac239 Vif elicits a curiously wide range of APOBEC3 degradation capabilities that include degradation of several human APOBEC3s and even human APOBEC3B, a non-HIV-1-restricting APOBEC3 enzyme. To better understand the molecular determinants of the interaction between SIVmac239 Vif and human APOBEC3B, we analyzed an extensive series of mutants. We found that SIVmac239 Vif interacts with the N-terminal domain of human APOBEC3B and, interestingly, that this occurs within a structural region homologous to the HIV-1 Vif interaction surface of human APOBEC3G. An alanine scan of SIVmac239 Vif revealed several residues required for human APOBEC3B degradation activity. These residues overlap HIV-1 Vif surface residues that interact with human APOBEC3G and are distinct from those that engage APOBEC3F or APOBEC3H. Overall, these studies indicate that the molecular determinants of the functional interaction between human APOBEC3B and SIVmac239 Vif resemble those between human APOBEC3G and HIV-1 Vif. These studies contribute to the growing knowledge of the APOBEC-Vif interaction and may help guide future efforts to disrupt this interaction as an antiviral therapy or exploit the interaction as a novel strategy to inhibit APOBEC3B-dependent tumor evolution.IMPORTANCE Primate APOBEC3 proteins provide innate immunity against retroviruses such as HIV and SIV. HIV-1, the primary cause of AIDS, utilizes its Vif protein to specifically counteract restrictive human APOBEC3 enzymes. SIVmac239 Vif exhibits a much wider range of anti-APOBEC3 activities that includes several rhesus macaque enzymes and extends to multiple proteins in the human APOBEC3 repertoire, including APOBEC3B. Understanding the molecular determinants of the interaction between SIVmac239 Vif and human APOBEC3B adds to existing knowledge on the APOBEC3-Vif interaction and has potential to shed light on what processes may have shaped Vif functionality over evolutionary time. An intimate understanding of this interaction may also lead to a novel cancer therapy because, for instance, creating a derivative of SIVmac239 Vif that specifically targets human APOBEC3B could be used to suppress tumor genomic DNA mutagenesis by this enzyme, slow ongoing tumor evolution, and help prevent poor clinical outcomes.

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Amino-terminal region of the human immunodeficiency virus type 1 nucleocapsid is required for human APOBEC3G packaging.

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