Ultrastructure of human retroviruses

122

The human T-cell leukemia virus type 1 (HTLV-1) Gag polyprotein contains two adjacent proline-rich motifs (sequence PPPYEPTAP) in the C terminus of the matrix domain. Proline-to-alanine mutations were introduced into either or both motifs of HTLV-1 to determine the effect on the release of HTLV-1 virus-like particles from 293T cells. The release of both single mutants was significantly reduced, whereas a double mutation in both motifs abolished the release of the HTLV-1 particles. Two-hybrid and in vitro binding assays showed that the HTLV-1 Gag polyprotein binds both Tsg101 and Nedd4 proteins. The interaction with HTLV-1 Gag required the central WW domain of Nedd4 and the ubiquitin enzyme variant (UEV) domain of Tsg101. We expressed various fragments of Nedd4 and Tsg101 proteins in 293T cells and tested for their ability to interfere with virion release mediated by the HTLV-1 Gag-Pro polyprotein. Fragments consisting of the N-terminal UEV domain of Tsg101 and the central WW and C-terminal Hect domains of Nedd4 protein all caused transdominant inhibition of HTLV-1 particle release. Similarly, inhibition of the proteasome significantly decreased HTLV-1 particle release. Furthermore, the WW domain overexpression caused an early arrest of HTLV-1 particle morphogenesis before the membrane is deformed into the typical half-shell structure. This result suggests that Nedd4 is involved early in budding of HTLV-1.

mentioning

confidence: 99%

PPPYEPTAP Motif Is the Late Domain of Human T-Cell Leukemia Virus Type 1 Gag and Mediates Its Functional Interaction with Cellular Proteins Nedd4 and Tsg101

Bouamr

Melillo

Wang

et al. 2003

122

“…One explanation for the difference between HIV-1 and HIV-2 could be the number and accessibility of Env spikes present on the virion. HIV-2 spikes have been reported to be more prominent and stable after budding (42,43), whereas the number of spikes on the HIV-1 particle drops immediately after budding and during maturation (44)(45)(46)(47). Given the nonfunctionality of some of these spikes (48), the type of C1q-IgG binding required for the optimal complement effect can be predicted to be fairly low in the case of HIV-1.…”

Section: Discussionmentioning

confidence: 99%

Effect of Complement on HIV-2 Plasma Antiviral Activity Is Intratype Specific and Potent

Şahin

Holmgren

Sheik-Khalil

et al. 2013

Human immunodeficiency virus type 2 (HIV-2)-infected individuals develop immunodeficiency with a considerable delay andtransmit the virus at rates lower than HIV-1-infected persons. Conceivably, comparative studies on the immune responsiveness of HIV-1-and HIV-2-infected hosts may help to explain the differences in pathogenesis and transmission between the two types of infection. Previous studies have shown that the neutralizing antibody response is more potent and broader in HIV-2 than in HIV-1 infection. In the present study, we have examined further the function of the humoral immune response and studied the effect of complement on the antiviral activity of plasma from singly HIV-1-or HIV-2-infected individuals, as well as HIV-1/ HIV-2 dually infected individuals. The neutralization and antibody-dependent complement-mediated inactivation of HIV-1 and HIV-2 isolates were tested in a plaque reduction assay using U87.CD4.CCR5 cells. The results showed that the addition of complement increased intratype antiviral activities of both HIV-1 and HIV-2 plasma samples, although the complement effect was more pronounced with HIV-2 than HIV-1 plasma. Using an area-under-the-curve (AUC)-based readout, multivariate statistical analysis confirmed that the type of HIV infection was independently associated with the magnitude of the complement effect. The analyses carried out with purified IgG indicated that the complement effect was largely exerted through the classical complement pathway involving IgG in both HIV-1 and HIV-2 infections. In summary, these findings suggest that antibody binding to HIV-2 structures facilitates the efficient use of complement and thereby may be one factor contributing to a strong antiviral activity present in HIV-2 infection.

“…In macrophages, HIV-1 Gag is present on and buds from internal membranes that resemble MVBs (28,32,33,35). However, in T cells and most permissive tissue culture cell lines, HIV-1 Gag is primarily localized to the plasma membrane, the site for virus assembly and release (7,15,26,29,30,32). It is not known how Gag recruits MVB proteins to the plasma membrane, and it is not understood how Gag is targeted to MVBs in macrophages.…”

mentioning

confidence: 99%

Human Immunodeficiency Virus Type 1 Gag Contains a Dileucine-Like Motif That Regulates Association with Multivesicular Bodies

Lindwasser

Resh

2004

Multivesicular bodies (MVBs) are cholesterol-enriched organelles formed by the endocytic pathway. The topology of vesicle formation in MVBs is identical to that of retroviral budding from the plasma membrane, and budding of human immunodeficiency virus type 1 (HIV-1) into MVBs in macrophages has recently been visualized. The Gag proteins from HIV-1, as well as many other retroviruses, contain short motifs that mediate interactions with MVBs and other endocytic components, suggesting that Gag proteins directly interface with the endocytic pathway. Here, we show that HIV-1 Gag contains an internalization signal that promotes endocytosis of a chimeric transmembrane fusion protein. Mutation of this motif within Gag strongly inhibits virus-like particle production. Moreover, wild-type Gag, but not the internalization-defective mutation, can be induced to accumulate within CD63-positive MVBs by treatment of cells with U18666A, a drug that redistributes cholesterol from the plasma membrane to MVBs. We propose that HIV-1 Gag contains a signal that promotes interaction with the cellular endocytic machinery and that the site of particle production is regulated by the subcellular distribution of cholesterol.