Morphogenesis of recombinant HIV-2 gag core particles

HIV-2 and its role in conglutinated approach towards Acquired Immunodeficiency Syndrome (AIDS) Vaccine Development

Acquired Immunodeficiency Syndrome (AIDS) is one of the most critically acclaimed endemic diseases, caused by two lentiviruses HIV-1 and 2. HIV-2 displays intimate serological and antigenic resemblance to Simian Immunodeficiency Virus (SIV) along with less pathogenicity, lower infectivity and appreciable cross reactivity with HIV-1 antigens. The present era is confronted with the challenge to fabricate a vaccine effective against all clades of both the species of HIV. But vaccine development against HIV-1 has proven highly intricate, moreover the laborious and deficient conventional approaches has slackened the pace regarding the development of new vaccines. These concerns may be tackled with the development of HIV-2 vaccine as a natural control of HIV-1 that has been found in ancestors of HIV-2 i.e. African monkeys, mangabeys and macaques. Thereby, suggesting the notion of cross protection among HIV-2 and HIV-1. Assistance of bioinformatics along with vaccinomics strategy can bring about a quantum leap in this direction for surpassing the bottleneck in conventional approaches. These specifics together can add to our conception that HIV-2 vaccine design by in silico strategy will surely be a constructive approach for HIV-1 targeting.

Differential budding efficiencies of human T-cell leukemia virus type I (HTLV-I) Gag and Gag-Pro polyproteins from insect and mammalian cells

In this study, we examined the ability of human T-cell leukemia virus type I (HTLV-I) Gag and Gag-Pro to assemble immature virus-like particles (VLPs) and bud from insect and mammalian cells. Transmission electron microscopy of insect cells infected with a recombinant baculovirus carrying the entire gag gene revealed that Pr53(Gag) is targeted to the plasma membrane, where it extensively accumulates and forms electron-dense evaginations. However, no particles could be detected either inside the cells or in the culture supernatants. With the Gag-Pro-expressing construct, we observed HTLV-I-specific cytoplasmic proteolysis of the Gag precursor, but again no particle released in the culture supernatants. Transmission electron microscopic analysis of insect cells expressing Gag-Pro polyprotein revealed large vacuoles in the cytoplasm and no budding particles at the plasma membrane. In contrast, human immunodeficiency virus type 1 Gag polyprotein expressed in insect cells is able to release VLPs. These data showed that unlike other retroviruses, Pr53(Gag) is unable to be released as immature VLPs from insect cells. To determine whether the block in particle budding and release is due to an intrinsic property of Pr53(Gag) or the absence of essential cellular factors in insect cells, we expressed Gag and Gag-Pro polyproteins in human 293 cells. The results indicate that Pr53(Gag) and p24 capsid are released within particles into the culture supernatants of human 293 cells. We found that the myristylation of the N-terminal glycine residue is essential for Gag release. Altogether, these results strongly suggest that the proper assembly of HTLV-I particles is dependent on mammalian host cell factors.

The envelope glycoprotein of human immunodeficiency virus type 2 enhances viral particle release: a Vpu-like factor?

The Vpu protein is a human immunodeficiency virus type 1 (HIV-1)-specific accessory protein that is required for the efficient release of viral particles from infected cells. Even though HIV-2 does not encode Vpu, we found that this virus is nevertheless capable of efficiently releasing virus particles. In fact, the rate of virus release from HeLa cells transfected with a full-length molecular clone of HIV-2, ROD10, was comparable to that observed for the vpu+ HIV-1 NL4-3 isolate and was not further enhanced by expression of Vpu in trans. However, consistent with previous observations showing that HIV-2 particle release is Vpu responsive in the context of HIV-1/HIV-2 chimeric constructs; exchanging the gag-pol region of NL4-3 with the corresponding region from pROD10 rendered the resulting chimeric virus Vpu responsive. Our finding that the responsiveness of HIV-2 particle release to Vpu is context dependent suggested the presence of a Vpu-like factor(s) encoded by HIV-2. Using chimeric proviruses encoding HIV-2 gag and pol in the context of the HIV-1 provirus that were coexpressed with subgenomic HIV-2 constructs, we found that the HIV-2 envelope glycoprotein had the ability to enhance HIV-2 particle release with an efficiency comparable to that of the HIV-1 Vpu protein. Conversely, inactivation of the HIV-2 env gene in the original ROD10 clone resulted in a decrease in the rate of viral particle release to a level that was comparable to that of Vpu-deficient HIV-1 isolates. Providing the wild-type envelope in trans rescued the particle release defect of the ROD10 envelope mutant. Thus, unlike HIV-1, which encodes two separate proteins to regulate virus release or to mediate viral entry, the HIV-2 Env protein has evolved to perform both functions.

Cell line-dependent release of HIV-like gag particles after infection of mammalian cells with recombinant vaccinia viruses

We investigated the production of Gag particles by Vero, CV-1, or 1D cells infected with different vaccinia virus recombinants expressing HIV gag or gag-pol genes. Immunoblots of (centrifuged) culture media from 1D cells infected with vMM5, a vaccinia virus recombinant expressing the HIV-2 gag-pol genes, revealed the presence of abundant particles that contained (mostly processed) Gag antigens. In contrast, Gag particles were found only in low amounts in the culture medium from Vero cells infected with the same HIV gag-pol vaccinia virus recombinant; the Gag precursor remained associated with the infected Vero cells and was efficiently processed. This low excretion of Gag particles after infection of Vero cells with vMM5 was also demonstrated by assays of reverse transcriptase activity in the pellet of centrifuged culture medium. Cell fractionation showed that Gag proteins were predominantly found in the membrane fraction from both 1D and Vero cells. Electron microscopy observations of 1D or of Vero cells infected with vMM5 vaccinia virus recombinant revealed in both cases the presence of particles budding at the plasma membrane. However, the shape of the budding particles was different in the two cell lines, with immature forms present in the membrane from the infected Vero cells. An inefficient excretion of Gag particles was also observed after infection of Vero cells with different vaccinia virus recombinants expressing either an uncleaved HIV-2 Gag protein or the HIV-1 gag-pol genes, as judged both by immunoblot and reverse transcriptase activity assays.(ABSTRACT TRUNCATED AT 250 WORDS)

Epitope mapping of a monoclonal antibody which binds HIV-1 Gag and not the Gag-derived proteins

Monoclonal antibody (MAb) 1G12 binds the uncleaved HIV-1 Gag polypeptide (p55), but fails to recognize the final products of the proteolytic processing [Sarubbi, E. et al. (1991) FEBS Lett. 279, 265-269]. In this report we show that binding of MAb 1G12 to a 110-residue Gag fragment containing the p17-p24 cleavage site prevents proteolysis of this site by the HIV-1 protease. Competition studies with synthetic peptides have been performed to map the binding site of MAb 1G12 on Gag. The antibody recognizes a sequential epitope that spans the HIV-1 protease cleavage site; determinants located on both p17 and p24 are required for antibody binding. MAb 1G12 is also shown to lack any cross-reactivity with other HIV-1 protease cleavage sites.

Generation, characterization and cross-reactivities of monoclonal antibodies against the p24 core protein and the gp130 envelope glycoprotein of HIV-2ben

The purpose of this study was to characterize antigenic determinants on structural polypeptides of human immunodeficiency virus type 2 (HIV-2ben). Therefore, three HIV-2-specific monoclonal antibodies (mAbs) against the p24 core protein (gag) and one mAb against the gp130 envelope glycoprotein (env) were produced. In addition to p24 the anti-core mAbs recognized the primary translation product of the viral gag gene p55 and an intermediate cleavage product p41. Core mAbs cross-reacted with another HIV-2 isolate (HIV-2rod), and several simian immunodeficiency viruses (SIVagm TYO7 and SIVmac), but not with SIVmnd and the HIV-1 isolates investigated (HIV-1han and HIV-1lai). The env mAb cross-reacted with HIV-2rod and SIVmac but not with SIVagm, SIVmnd or HIV-1. In competition assays and with epitope mapping possible binding sites for the mAbs were identified. The processing of HIV-2 core proteins is compared in retrovirus-infected T cell lines and during the expression by recombinant vaccinia virus. Finally, the mAb XIV DC10 which recognized a highly conserved epitope could be useful for an assay to detect HIV-1 and HIV-2 simultaneously. II D8 is the first mAb raised against HIV-2 env glycoprotein.