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Query: UMLS:C0021051 (immunodeficiency)
 71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The envelope (env) glycoprotein of human immunodeficiency virus 1 (HIV-1), initially synthesized as a precursor molecule termed gp160, is cleaved into two noncovalently associated subunits prior to delivery to the plasma membrane. We have studied the oligomeric structure of this protein using chemical cross-linking, velocity gradient sedimentation, and SDS-resistance. We find that gp160 forms stable homodimers after synthesis. After cleavage to gp120/gp41 the molecule becomes less stable to detergent solubilization and centrifugation but remains dimeric. Interactions between the 129 amino terminal residues in the ectodomains of adjoining gp41 subunits are both sufficient and necessary for assembly. In addition, tetramers composed of two dimers were also formed. Larger structures were not observed. The tetrameric paramyxovirus F protein, which has structural and functional similarities to the HIV-1 env protein, also forms a dimer of dimers.
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PMID:The assembly of the HIV-1 env glycoprotein into dimers and tetramers. 178 45

Heterotypic adhesion of T lymphocytes to monocytes, B lymphocytes, or other target cells is mainly mediated by LFA-1 and CD2 molecules. Low-affinity binding of resting T cells can be transiently up-regulated by cross-linking of CD3. We have previously found that binding of specific ligands to CD4 can down-regulate adhesion of resting T cells to B cells. We now show that the enhanced adhesiveness of CD4+ T cells induced by CD3 cross-linking using plastic-bound anti-CD3 antibody can also be inhibited by several CD4 ligands. i.e. anti-CD4 antibodies, the gp160 env protein of human immunodeficiency virus, as well as by putative CD4 ligands, i.e. synthetic peptides analogous to the gp160-binding site to CD4 (positions 418-434 and 449-464) and a 12-mer synthetic peptide (DR-12) analogous to positions 35-46 of HLA class II beta subunit and including the highly conserved Arg-Phe-Asp-Ser (RFDS) sequence. After CD3 cross-linking, maximal binding of T cells to HLA class II-positive and -negative B cells was similar, although binding to HLA class II-negative B cells was more prolonged. T cells that were passively induced to up-regulate adhesion by binding of a CD11a-specific antibody NKIL16, known to enhance LFA-1-dependent adhesiveness, were less sensitive to the inhibitory effect of the DR-12 peptide, whereas the inhibitory effects of gp160 were preserved. The kinetics of adhesion of NKIL16-pretreated T cells was not influenced by HLA class II expression at the B cell surface. Together, these results strongly suggest that CD4-HLA class II interaction may down-regulate low-affinity adhesion of resting T cells and, to some extent, high-affinity adhesion of T cells actively induced by CD3 cross-linking but not passively induced by an anti-CD11a antibody.
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PMID:Regulation of LFA-1-mediated T cell adhesion by CD4. 182 86

The effects of C-terminal and internal deletions on the synthesis, transport, biological properties, and antigenicity of the human immunodeficiency virus type 1 envelope protein were determined. A family of recombinant vaccinia viruses that express N-terminal overlapping env proteins of 204, 287, 393, 502 (full-length gp120), 635, 747, and 851 (full-length gp160) amino acids was constructed. All of the proteins were detected in intra- and extracellular forms which differed in the extent of glycosylation. The 747- and 851-amino-acid proteins were cleaved, were expressed on the surface of infected cells, and bound CD4. The 635-amino-acid env protein was cleaved inefficiently, and both the precursor and product were secreted, indicating absence of the transmembrane sequence. The 635- as well as the 502-amino-acid protein, which was also largely secreted, could still bind CD4. Unexpectedly, the 393-amino-acid protein was anchored in the plasma membrane, but neither it nor smaller proteins bound to soluble CD4. When amino acids at the gp120-gp41 junction were deleted, proteolytic cleavage of gp160 did not occur. Nevertheless, gp160 was inserted into the plasma membrane and bound soluble CD4. The predominant conserved B-cell epitopes were mapped to gp41 and the C terminus of gp120, whereas cytotoxic T-cell epitopes were distributed throughout the length of the glycoproteins.
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PMID:Biological and immunological properties of human immunodeficiency virus type 1 envelope glycoprotein: analysis of proteins with truncations and deletions expressed by recombinant vaccinia viruses. 198 2

A total of 81 cell clones persistently infected with the LAV-1 or HTLV-IIIB strain of human immunodeficiency virus type 1 (HIV-1) was isolated from cells which were obtained by serial passage of some proliferating MT-4 cells after a drastic cytolysis of most cells by HIV-1-infection. These cell clones were classified into 8 types (I to VIII) in terms of the expression of HIV-1 antigens, syncytium formation capacity, and reverse transcriptase activity and infectivity of virus particles in the culture fluid. Type I cell clones were producers of infectious HIV-1 particles, while types II to VIII cell clones did not produce infectious HIV-1 or were producers of uninfectious defective HIV-1 particles. Immunoprecipitation followed by SDS-polyacrylamide gel electrophoresis (PAGE) showed that the gag precursor protein in L-2 cell clone (type IV) was not cleaved to mature gag proteins, while the env precursor protein on L-3 cell clone (type III) was not cleaved to mature env protein. H-7 cell clone (type VIII) did not express any HIV-1 antigen. All these cell clones after the superinfection with infectious HIV-1 synthesized intact gag and env proteins, which were, at least in part, related to the HIV-1 genome persistently present in the cell clones before the superinfection, resulting in production of infectious HIV-1. For example, it was found that L-2 cell clone contained a single copy of the LAV-1 genome per haploid cell and produced doughnut-shaped particles. On the other hand, the cell clone isolated from the L-2 cell clone superinfected with infectious HTLV-IIIB contained the integrated HTLV-IIIB genome in addition to the LAV-1 genome present before the superinfection, and produced intact HIV-1 particles in addition to doughnut-shaped particles from a single cell. These results indicate that complementation and/or genetic recombination events in the superinfected cells may account for the production of infectious intact HIV-1 virions.
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PMID:Production of infectious particles from defective human immunodeficiency virus type 1 (HIV-1)-producing cell clones by superinfection with infectious HIV-1. 200 Nov 75

To gain insights into the structure-function relationship of the envelope (env) glycoprotein of the human immunodeficiency virus type 1 (HIV-1) we have generated a vaccinia virus (VV) recombinant (VV-14kENV) that expresses a fusion protein (14k-env) consisting of the VV 14-kDa envelope protein (110 amino acids) fused at the C-terminus with HIV-1 env protein (816 amino acids). The 14k-env protein displayed unique structural properties in virus-infected cells. This protein was recognized by 14 kDa-specific antisera as well as HIV-1 env antisera. It was not cleaved during virus infection of cultured cells of various origins, it was stable, it was not released to the medium, and it was not incorporated into virions. Instead of a predicted 174-kDa protein, two proteins of about 110 and 100 kDa were observed. The size reduction of the fusion protein was due to limited glycosylation (110 kDa) and formation of unglycosylated protein (100 kDa). The 14k-env protein formed oligomeric structures and was exposed on the cell surface after virus infection. When mice were inoculated with the recombinant virus that expresses the 14K-env fusion protein, humoral immune response against gp160 was observed. Our findings suggest that 14k-env protein might display novel immunogenic properties.
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PMID:Structural properties of HIV-1 Env fused with the 14-kDa vaccinia virus envelope protein. 201 47

The expression of human immunodeficiency virus 1 (HIV-1) envelope glycoprotein products was studied in cells transfected with env gene constructs transcribed from an SV40 promoter. Gene constructs possessing the complete tat, rev (tat+ rev+) and env genes were transiently expressed in COS-1 cells as precursor SU-TM (gp160), SU.TM (gp120 x 41), and nucleolar rev protein. In addition, envelope glycoprotein was detected on the surface of those transfected COS-1 cells expressing abundant levels of env protein. Transfected constructs possessing a mutated tat translational initiation codon (tat-rev+) were expressed in COS-1 cells with at least a 10-fold increase in the level of envelope glycoprotein expression compared to the analogous constructs with an intact tat AUG codon (tat+ rev+). Mutation of the rev initiation codon (tat+ rev-) and (tat-rev-) resulted in no detectable expression of env products but expression of these proteins could be rescued by co-transfection of a cDNA encoding the rev gene. Subgenomic tat/rev transcripts were detected following transfection of all of the gene constructs indicating splicing of the env mRNAs transcribed from a heterologous promoter. Unspliced env transcripts were only detected in the cytoplasm of cells transfected with (rev+) constructs or with the (tat- rev-) construct in the presence of the rev cDNA supplied in trans. In contrast, unspliced transcripts were detected in the nuclear and total cellular RNA of all transfected cells. Expression of rev protein was localized to the nucleolus of transfected COS-1 cells. These results indicate that the export of unspliced env mRNA to the cytoplasm is facilitated by the expression of rev. Following env synthesis, the conversion of SU-TM (gp160) to SU.TM (gp120 x 41) was not quantitative. After a 20-h pulse-chase, only 40% of the SU-TM (gp160) present at the start of the chase period was subsequently accountable as mature SU (gp120), and approximately 30% of the detectable SU (gp120) was found in the culture medium of transfected COS-1 cells. The findings indicate that the surface expression of SU.TM (gp120 x 41) derived from heterologous gene transcripts is modulated (i) the co-expression of rev, (ii) the efficiency of proteolytic processing of SU-TM (gp160), and (iii) the degree of SU (gp120) shedding and/or secretion from the cell.
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PMID:Expression of human immunodeficiency virus 1 (HIV-1) envelope gene products transcribed from a heterologous promoter. Kinetics of HIV-1 envelope processing in transfected cells. 222 68

The envelope (env) glycoprotein of human immunodeficiency virus type 1 (HIV-1) consists of two noncovalently associated subunits, gp120 and gp41, that are formed gradient sedimentation, polyacrylamide gel electrophoresis, gradient sedimentation, polyacrylamide gel electrophoresis, and chemical cross-linking, we show that gp160 is synthesized as a monomer and subsequently forms stable homodimers. The molecule remains dimeric after cleavage to gp120/gp41 but is less stable to detergent solubilization and centrifugation. Analysis of wild-type and mutated env proteins indicated that interactions between the ectodomain regions of adjoining gp41 subunits are important for dimer formation and stability. A higher-order oligomeric form was also recovered, probably a tetramer consisting of two noncovalently associated dimers. The proposed subunit composition of the HIV-1 env protein is identical to that previously observed for the paramyxovirus envelope proteins F and HN.
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PMID:Oligomeric structure of the human immunodeficiency virus type 1 envelope glycoprotein. 230 May 52

The envelope (env) glycoproteins of human immunodeficiency viruses type 1 (HIV-1) and type 2 (HIV-2) form dimers shortly after synthesis. Analysis of the simian immunodeficiency virus (SIV) env protein expressed by a recombinant vaccinia virus revealed that it, too, forms stable homodimers. When the HIV-1 and SIV env proteins or the HIV-1 and HIV-2 env proteins were coexpressed in the same cells, heterodimers were formed. Thus, the env proteins of HIV-1, HIV-2, and SIV possess a functionally conserved domain involved in subunit-subunit recognition and assembly that likely involves the ectodomain of gp41.
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PMID:Human immunodeficiency virus types 1 and 2 and simian immunodeficiency virus env proteins possess a functionally conserved assembly domain. 235 32

Human immunodeficiency virus (HIV) exhibits immunological hypervariability, which has been an obstacle to successful production of effective anti-HIV vaccines. In this study, we estimated patterns of nucleotide and amino acid substitutions in the env gene of HIVs, with the aim of finding characteristics of the mechanism which generates the immunological diversity of the env protein of HIVs. We found that nucleotide changes between A and G are predominant compared to those between other nucleotides. Since this feature is consistent with the pattern of nucleotide substitutions of other retroviral genes but is quite different from those of most eukaryotic genes, a high rate of nucleotide substitution between A and G appears to be specific for retroviruses including HIVs. We discuss the biological relationship between this biased substitution and the mechanism generating hypervariability of epitopes on the env protein of HIVs.
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PMID:Patterns of nucleotide substitutions and implications for the immunological diversity of human immunodeficiency virus. 275 54

Nine different recombinant clones spanning various regions of the bovine immunodeficiency-like virus (BIV) envelope gene open reading frame were generated. These clones span the entire external glycoprotein as well as the transmembrane glycoprotein region. These proteins were expressed as fusions to the TrpE protein in E. coli. The levels of recombinant protein expressed varied, some clones expressed enough protein that can be detected in a Coomassie blue-stained gel, whereas other proteins could only be detected by Western blot analyses. A recombinant env protein representing the extracellular domain of the env protein was detected by BIV-infected bovine sera. In addition, a 134 amino acid peptide which may represent a major immunoreactive epitope was identified. This peptide is located at the amino terminus of the transmembrane glycoprotein and was specifically recognized by all BIV-infected calf sera tested. The identification of this epitope and the use of recombinant envelope protein will enable us to develop a more effective screening test to study the epidemiology of BIV infection.
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PMID:Use of TrpE fusion protein to identify antigenic domains within the BIV envelope protein. 752 Sep 16


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