The Mechanism of Budding of Retroviruses from Cell Membranes

Retroviruses have evolved a mechanism for the release of particles from the cell membrane that appropriates cellular protein complexes, referred to as ESCRT-I, -II, -III, normally involved in the biogenesis of multivesicular bodies. Three different classes of late assembly (L) domains encoded in Gag, with core sequences of PPXY, PTAP, and YPXL, recruit different components of the ESCRT machinery to form a budding complex for virus release. Here, we highlight recent progress in identifying the role of different ESCRT complexes in facilitating budding, ubiquitination, and membrane targeting of avian sarcoma and leukosis virus (ASLV) and human immunodeficiency virus, type 1 (HIV-1). These findings show that retroviruses may adopt parallel budding pathways by recruiting different host factors from common cellular machinery for particle release.

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The Mason-Pfizer Monkey Virus PPPY and PSAP Motifs Both Contribute to Virus Release

Journal of Virology ◽

10.1128/jvi.77.17.9474-9485.2003 ◽

2003 ◽

Vol 77 (17) ◽

pp. 9474-9485 ◽

Cited By ~ 97

Author(s):

Eva Gottwein ◽

Jochen Bodem ◽

Barbara Müller ◽

Ariane Schmechel ◽

Hanswalter Zentgraf ◽

...

Keyword(s):

Cellular Protein ◽

Membrane Curvature ◽

Mutant Virus ◽

Dependent Manner ◽

Virus Release ◽

Immunodeficiency Virus ◽

Ptap Motif ◽

Hiv 1

ABSTRACT Late (L) domains are required for the efficient release of several groups of enveloped viruses. Three amino acid motifs have been shown to provide L-domain function, namely, PPXY, PT/SAP, or YPDL. The retrovirus Mason-Pfizer monkey virus (MPMV) carries closely spaced PPPY and PSAP motifs. Mutation of the PPPY motif results in a complete loss of virus release. Here, we show that the PSAP motif acts as an additional L domain and promotes the efficient release of MPMV but requires an intact PPPY motif to perform its function. Examination of HeLaP4 cells expressing PSAP mutant virus by electron microscopy revealed mostly late budding structures and chains of viruses accumulating at the cell surface with little free virus. In the case of the PPPY mutant virus, budding appeared to be mostly arrested at an earlier stage before induction of membrane curvature. The cellular protein TSG101, which interacts with the human immunodeficiency virus type 1 (HIV-1) PTAP L domain, was packaged into MPMV in a PSAP-dependent manner. Since TSG101 is crucial for HIV-1 release, this result suggests that the Gag-TSG101 interaction is responsible for the virus release function of the MPMV PSAP motif. Nedd4, which has been shown to interact with viral PPPY motifs, was also detected in MPMV particles, albeit at much lower levels. Consistent with a role of VPS4A in the budding of both PPPY and PTAP motif-containing viruses, the overexpression of ATPase-defective GFP-VPS4A fusion proteins blocked both wild-type and PSAP mutant virus release.

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Structure, Function, and Interactions of the HIV-1 Capsid Protein

Life ◽

10.3390/life11020100 ◽

2021 ◽

Vol 11 (2) ◽

pp. 100

Author(s):

Eric Rossi ◽

Megan E. Meuser ◽

Camille J. Cunanan ◽

Simon Cocklin

Keyword(s):

Life Cycle ◽

Capsid Protein ◽

Adaptor Proteins ◽

Restriction Factors ◽

Gag Polyprotein ◽

Immunodeficiency Virus ◽

Host Cell Factors ◽

Hiv 1

The capsid (CA) protein of the human immunodeficiency virus type 1 (HIV-1) is an essential structural component of a virion and facilitates many crucial life cycle steps through interactions with host cell factors. Capsid shields the reverse transcription complex from restriction factors while it enables trafficking to the nucleus by hijacking various adaptor proteins, such as FEZ1 and BICD2. In addition, the capsid facilitates the import and localization of the viral complex in the nucleus through interaction with NUP153, NUP358, TNPO3, and CPSF-6. In the later stages of the HIV-1 life cycle, CA plays an essential role in the maturation step as a constituent of the Gag polyprotein. In the final phase of maturation, Gag is cleaved, and CA is released, allowing for the assembly of CA into a fullerene cone, known as the capsid core. The fullerene cone consists of ~250 CA hexamers and 12 CA pentamers and encloses the viral genome and other essential viral proteins for the next round of infection. As research continues to elucidate the role of CA in the HIV-1 life cycle and the importance of the capsid protein becomes more apparent, CA displays potential as a therapeutic target for the development of HIV-1 inhibitors.

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Role of Vif in Stability of the Human Immunodeficiency Virus Type 1 Core

Journal of Virology ◽

10.1128/jvi.74.23.11055-11066.2000 ◽

2000 ◽

Vol 74 (23) ◽

pp. 11055-11066 ◽

Cited By ~ 53

Author(s):

Åsa Öhagen ◽

Dana Gabuzda

Keyword(s):

Human Immunodeficiency Virus ◽

Dna Synthesis ◽

Virus Entry ◽

Wild Type ◽

The Core ◽

Immunodeficiency Virus ◽

The Stability ◽

Hiv 1

ABSTRACT The Vif protein of human immunodeficiency virus type 1 (HIV-1) is important for virion infectivity. Previous studies have shown thatvif-defective virions exhibit structural abnormalities in the virus core and are defective in the ability to complete proviral DNA synthesis in acutely infected cells. We developed novel assays to assess the relative stability of the core in HIV-1 virions. Using these assays, we examined the role of Vif in the stability of the HIV-1 core. The integrity of the core was examined following virion permeabilization or removal of the lipid envelope and treatment with various triggers, including S100 cytosol, deoxynucleoside triphosphates, detergents, NaCl, and buffers of different pH to mimic aspects of the uncoating and disassembly process which occurs after virus entry but preceding or during reverse transcription.vif mutant cores were more sensitive to disruption by all triggers tested than wild-type cores, as determined by endogenous reverse transcriptase (RT) assays, biochemical analyses, and electron microscopy. RT and the p7 nucleocapsid protein were released more readily from vif mutant virions than from wild-type virions, suggesting that the internal nucleocapsid is less stably packaged in the absence of Vif. Purified cores could be isolated from wild-type but not vif mutant virions by sedimentation through detergent-treated gradients. These results demonstrate that Vif increases the stability of virion cores. This may permit efficient viral DNA synthesis by preventing premature degradation or disassembly of viral nucleoprotein complexes during early events after virus entry.

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Removal of a Single N-Linked Glycan in Human Immunodeficiency Virus Type 1 gp120 Results in an Enhanced Ability To Induce Neutralizing Antibody Responses

Journal of Virology ◽

10.1128/jvi.01691-07 ◽

2007 ◽

Vol 82 (2) ◽

pp. 638-651 ◽

Cited By ~ 127

Author(s):

Yun Li ◽

Bradley Cleveland ◽

Igor Klots ◽

Bruce Travis ◽

Barbra A. Richardson ◽

...

Keyword(s):

Human Immunodeficiency Virus ◽

Neutralizing Antibodies ◽

Neutralizing Antibody ◽

Pronounced Increase ◽

Enhanced Sensitivity ◽

Subtype B ◽

Immunodeficiency Virus ◽

Hiv 1

ABSTRACT Glycans on human immunodeficiency virus (HIV) envelope protein play an important role in infection and evasion from host immune responses. To examine the role of specific glycans, we introduced single or multiple mutations into potential N-linked glycosylation sites in hypervariable regions (V1 to V3) of the env gene of HIV type 1 (HIV-1) 89.6. Three mutants tested showed enhanced sensitivity to soluble CD4. Mutant N7 (N197Q) in the carboxy-terminal stem of the V2 loop showed the most pronounced increase in sensitivity to broadly neutralizing antibodies (NtAbs), including those targeting the CD4-binding site (IgG1b12) and the V3 loop (447-52D). This mutant is also sensitive to CD4-induced NtAb 17b in the absence of CD4. Unlike the wild-type (WT) Env, mutant N7 mediates CD4-independent infection in U87-CXCR4 cells. To study the immunogenicity of mutant Env, we immunized pig-tailed macaques with recombinant vaccinia viruses, one expressing SIVmac239 Gag-Pol and the other expressing HIV-1 89.6 Env gp160 in WT or mutant forms. Animals were boosted 14 to 16 months later with simian immunodeficiency virus gag DNA and the cognate gp140 protein before intrarectal challenge with SHIV89.6P-MN. Day-of-challenge sera from animals immunized with mutant N7 Env had significantly higher and broader neutralizing activities than sera from WT Env-immunized animals. Neutralizing activity was observed against SHIV89.6, SHIV89.6P-MN, HIV-1 SF162, and a panel of subtype B primary isolates. Compared to control animals, immunized animals showed significant reduction of plasma viral load and increased survival after challenge, which correlated with prechallenge NtAb titers. These results indicate the potential advantages for glycan modification in vaccine design, although the role of specific glycans requires further examination.

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Nutritional Contributions to the CNS Pathophysiology of HIV-1 Infection and Implications for Treatment

CNS Spectrums ◽

10.1017/s1092852900013122 ◽

2000 ◽

Vol 5 (4) ◽

pp. 61-72 ◽

Cited By ~ 5

Author(s):

Teri T. Baldewicz ◽

Pim Brouwers ◽

Karl Goodkin ◽

Adarsh M. Kumar ◽

Mahendra Kumar

Keyword(s):

Disease Progression ◽

Causative Factor ◽

Nutritional Deficiencies ◽

Micronutrient Deficiencies ◽

Increased Risk ◽

Immunodeficiency Virus ◽

Nutritional Deficits ◽

Hiv 1

AbstractNutritional deficiencies are commonplace in patients with human immunodeficiency virus type 1 (HIV-1) infection, and recent research has indicated that nutritional factors may play an important role in the pathogenesis of HIV-1 disease. Although nutritional deficiencies are unlikely to be the primary causative factor in disease progression, they may contribute to cognitive dysfunction, neurologic abnormalities, mood disturbance, and immune dysregulation associated with HIV-1 infection. Furthermore, deficiencies of specific micronutrients have been associated with increased risk of HIV-1–associated mortality. This article will briefly summarize the role of macronutrient deficiency, the interactions of specific micronutrient deficiencies with neuropsychiatrie functioning, and the role of these factors in HIV-1 disease progression. Since recent research has shown that normalization of many nutritional deficits and supplementation beyond normal levels are associated with improvements in neuropsychiatrie functioning, potential treatment implications will also be discussed.

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Structure–functional analysis of human immunodeficiency virus type 1 (HIV-1) Vpr: role of leucine residues on Vpr-mediated transactivation and virus replication

Virology ◽

10.1016/j.virol.2004.07.013 ◽

2004 ◽

Vol 328 (1) ◽

pp. 89-100 ◽

Cited By ~ 16

Author(s):

Dineshkumar Thotala ◽

Elizabeth A. Schafer ◽

Biswanath Majumder ◽

Michelle L. Janket ◽

Marc Wagner ◽

...

Keyword(s):

Functional Analysis ◽

Human Immunodeficiency Virus ◽

Virus Replication ◽

Human Immunodeficiency Virus Type ◽

Virus Type ◽

Immunodeficiency Virus ◽

Hiv 1

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Role of Cell Surface Glycosaminoglycans of Human T Cells in Human Immunodeficiency Virus Type-1 (HIV-1) Infection

Microbiology and Immunology ◽

10.1111/j.1348-0421.1996.tb01148.x ◽

1996 ◽

Vol 40 (11) ◽

pp. 827-835 ◽

Cited By ~ 55

Author(s):

Yukako Ohshiro ◽

Tsutomu Murakami ◽

Kazuhiro Matsuda ◽

Kiyoshi Nishioka ◽

Keiichi Yoshida ◽

...

Keyword(s):

Human Immunodeficiency Virus ◽

T Cells ◽

Cell Surface ◽

Human Immunodeficiency Virus Type ◽

Virus Type ◽

Human T Cells ◽

Immunodeficiency Virus ◽

Hiv 1

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Proline Residues within Spacer Peptide p1 Are Important for Human Immunodeficiency Virus Type 1 Infectivity, Protein Processing, and Genomic RNA Dimer Stability

Journal of Virology ◽

10.1128/jvi.76.22.11245-11253.2002 ◽

2002 ◽

Vol 76 (22) ◽

pp. 11245-11253 ◽

Cited By ~ 31

Author(s):

Melissa K. Hill ◽

Miranda Shehu-Xhilaga ◽

Suzanne M. Crowe ◽

Johnson Mak

Keyword(s):

Protein Processing ◽

Viral Infectivity ◽

Genomic Rna ◽

Stem Loop ◽

Altered Protein ◽

Immunodeficiency Virus ◽

Rna Dimer ◽

Hiv 1

ABSTRACT The full-length human immunodeficiency virus type 1 (HIV-1) mRNA encodes two precursor polyproteins, Gag and GagProPol. An infrequent ribosomal frameshifting event allows these proteins to be synthesized from the same mRNA in a predetermined ratio of 20 Gag proteins for each GagProPol. The RNA frameshift signal consists of a slippery sequence and a hairpin stem-loop whose thermodynamic stability has been shown in in vitro translation systems to be critical to frameshifting efficiency. In this study we examined the frameshift region of HIV-1, investigating the effects of altering stem-loop stability in the context of the complete viral genome and assessing the role of the Gag spacer peptide p1 and the GagProPol transframe (TF) protein that are encoded in this region. By creating a series of frameshift region mutants that systematically altered the stability of the frameshift stem-loop and the protein sequences of the p1 spacer peptide and TF protein, we have demonstrated the importance of stem-loop thermodynamic stability in frameshifting efficiency and viral infectivity. Multiple changes to the amino acid sequence of p1 resulted in altered protein processing, reduced genomic RNA dimer stability, and abolished viral infectivity. The role of the two highly conserved proline residues in p1 (position 7 and 13) was also investigated. Replacement of the two proline residues by leucines resulted in mutants with altered protein processing and reduced genomic RNA dimer stability that were also noninfectious. The unique ability of proline to confer conformational constraints on a peptide suggests that the correct folding of p1 may be important for viral function.

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ADAR2 editing enzyme is a novel human immunodeficiency virus-1 proviral factor

Journal of General Virology ◽

10.1099/vir.0.028043-0 ◽

2011 ◽

Vol 92 (5) ◽

pp. 1228-1232 ◽

Cited By ~ 22

Author(s):

Margherita Doria ◽

Sara Tomaselli ◽

Francesca Neri ◽

Silvia Anna Ciafrè ◽

Maria Giulia Farace ◽

...

Keyword(s):

Human Immunodeficiency Virus ◽

Jurkat Cells ◽

Replication Process ◽

Adenosine Deaminases ◽

Immunodeficiency Virus ◽

Editing Enzyme ◽

Infectious Potential ◽

Hiv 1

The adenosine deaminases acting on RNA (ADAR) enzymes catalyse conversion of adenosine to inosine in dsRNA. A positive effect of ADAR1 on human immunodeficiency virus type 1 (HIV-1) replication has recently been reported. Here, we show that another ADAR enzyme, ADAR2, positively affects the replication process of HIV-1. We found that, analogously to ADAR1, ADAR2 enhances the release of progeny virions by an editing-dependent mechanism. However, differently from the ADAR1 enzyme, ADAR2 does not increase the infectious potential of the virus. Importantly, downregulation of ADAR2 in Jurkat cells significantly impairs viral replication. Therefore, ADAR2 shares some but not all proviral functions of ADAR1. These results suggest a novel role of ADAR2 as a viral regulator.

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