Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019693 (HIV)
 170,526 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The nucleocapsid protein NCp7 of human immunodeficiency virus type 1 (HIV-1), which has key functions in the virus life cycle, possesses two zinc fingers of the CX2CX4HX4C type characterized by three successive loops containing a tetrahedrally coordinated zinc atom. The replacement of any cysteine by a serine in either finger has been shown to result in the production of noninfectious viruses, probably by impairing the biological functions of NCp7. In order to more precisely elucidate the structural role of the zinc finger motif, His23 was replaced by Cys in the proximal finger of the peptide (13-64)NCp7 which retains NCp7 activities in vitro. The peptide Cys23(13-64)NCp7 was synthesized by solid phase and studied by 2D 1H NMR and molecular modeling. The His to Cys modification causes important structural modifications of the N-terminal zinc finger which impair the spatial proximity of the two zinc fingers as shown by the disappearance of several interresidue NOEs. The side chains of Val13, Lys14, Phe16, Thr24, Ala25, Trp37, Gln45, and Met46, which are thought to be involved in nucleic acid recognition, are no longer found clustered in the Cys23(13-64)NCp7 mutant as they are in the wild-type NCp7 structure. In vitro, Cys23(13-64)NCp7 is unable to tightly interact with the viral RNA or replication primer tRNA(Lys,3). The Cys23(NCp7) mutation was introduced into an infectious HIV-1 molecular clone, and virions produced upon DNA transfection into cells were analyzed for their viral protein and RNA compositions as well as for their infectivity. Results show that, while the Cys23(NCp7) mutation does not impair virion production, viruses contain a low amount of degraded viral RNA and are not infectious. These findings suggest that a bona fide conformation of the HIV-1 NCp7 is critical for the packaging of viral RNA, its stability in virions, and virus infectivity.
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PMID:1H NMR structure and biological studies of the His23-->Cys mutant nucleocapsid protein of HIV-1 indicate that the conformation of the first zinc finger is critical for virus infectivity. 791 87

CD26 is a lymphocyte cell surface antigen which is increased during T-cell activation and is also expressed in other tissues. It is an atypical serine protease belonging to the prolyl oligopeptidase family. CD26 has been implicated in a variety of biological functions including T-cell activation, cell-to-cell adhesion, and recently in HIV infection. This paper describes, through the isolation and partial sequencing of eight human CD26 genomic clones, the first information on the genomic organization of the prolyl oligopeptidase family. We have established that the human CD26 gene spans approximately 70 kilobases (kb) and contains 26 exons, ranging in size from 45 base pairs (bp) to 1.4 kb. The nucleotides that encode the serine recognition site (G-W-S-Y-G) are split between two exons. This clearly distinguishes the genomic organization of the prolyl oligopeptidase family from that of the classical serine protease family. The 5' flanking domain of the CD26 gene contains neither a TATA box nor a CAAT box, but a 300 bp region extremely rich in C and G (72%) contains potential binding sites for several transcriptional factors. The human CD26 gene encodes two messages sized at about 4.2 and 2.8 kb. These are both expressed at high levels in the placenta and kidney and at moderate levels in the lung and liver. Only the 4.2 kb mRNA was expressed at low levels in skeletal muscle, heart, brain, and pancreas. Fluorescence in situ hybridization on metaphase chromosome spreads located the human CD26 gene to the long arm of chromosome 2(2q24.3).
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PMID:Genomic organization, exact localization, and tissue expression of the human CD26 (dipeptidyl peptidase IV) gene. 792 37

Two groups of U937 promonocytic cells were obtained by limiting dilution cloning which differed strikingly in their ability to support human immunodeficiency virus 1 (HIV-1) replication. "Plus" clones replicated the virus efficiently, whereas "minus" clones did not. We examined these clones for differences in nuclear factor (NF)-kappa B activity which might account for the observed phenomenon. Stimulation of plus clones liberated the classical p50-p65 complex from cytoplasmic pools, whereas minus clones produced an apparently novel, faster-migrating complex, as judged by electrophoretic mobility shift assays. It is surprising that the faster-migrating complex was composed also of p50 and p65. However, the p65 subunit was COOH-terminally truncated, as shown by immunoprecipitation. The truncation resulted from limited proteolysis of p65 during cellular extraction which released particular lysosomal serine proteases, such as elastase, cathepsin G, and proteinase 3. These specific proteases are coordinately expressed and were present exclusively in the minus U937 clones, but not in the plus clones, as demonstrated in the case of cathepsin G. In addition, these proteases were detected in certain subclones of THP-1 and HL-60 cells and in primary monocytes, in each case correlating with the truncated from of p65. We demonstrate in vitro cleavage of p65 by purified elastase and cathepsin G. It is possible that particular serine proteases may have inhibiting effects on the replication of HIV-1 in myelo-monocytic cells. The data also demonstrate that special precautions must be taken when making extracts from myelo-monocytic cells.
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PMID:A family of serine proteases expressed exclusively in myelo-monocytic cells specifically processes the nuclear factor-kappa B subunit p65 in vitro and may impair human immunodeficiency virus replication in these cells. 793 Oct 77

We have used a combination of genetic and immunological techniques to explore how amino acid substitutions in the second conserved (C2) domain of gp120 from human immunodeficiency virus type 1 (HIV-1) affect the conformation of the protein. It was reported previously (R. L. Willey, E. K. Ross, A. J. Buckler-White, T. S. Theodore, and M. A. Martin. J. Viol. 63:3595-3600, 1989) that an asparagine-glutamine (N/Q) substitution at C2 residue 267 of HIV-1 NL4/3 reduced virus infectivity, but that infectivity was restored by a compensatory amino acid change (serine-glutamine; S/N) at residue 128 in the C1 domain. Here we show that the 267 N/Q substitution causes the abnormal exposure of a segment of C1 spanning residues 80 to 120, which compromises the integrity of the CD4-binding site. The reversion substitution at residue 128 restores the normal conformation of the C1 domain and recreates a high-affinity CD4-binding site. The gp120 structural perturbation caused by changes in C2 extends also to the C5 domain, and we show by immunological analysis that there is a close association between areas of the C1 and C5 domains. This association might be important for forming a complex binding site for gp41 (E. Helseth, U. Olshevsky, C. Furman, and J. Sodroski. J. Virol. 65:2119-2123, 1991). Segments of the C1 and C2 domains are predicted to form amphipathic alpha helices. We suggest that these helices might be packed together in the core of the folded gp120 molecule, that the 267 N/Q substitution disrupts this interdomain association, and that the 128 S/N reversion substitution restores it.
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PMID:Immunological evidence for interactions between the first, second, and fifth conserved domains of the gp120 surface glycoprotein of human immunodeficiency virus type 1. 793 65

The nef gene is conserved throughout the primate lentivirus family. Although dispensable in vitro, an important role for nef in vivo is suggested by the failure of SIV nef mutants to establish persistent viraemia. Although the biochemical function of the Nef protein remains equivocal, a consistent theme has emerged with the reproducible observation that Nef expression results in the down-modulation of the cell surface marker CD4. Down-modulation requires amino acid sequences within the cytoplasmic domain of CD4 but occurs by a mechanism distinct from the normal serine phosphorylation-dependent pathway. As CD4 is a transmembrane glycoprotein and Nef a myristoylated protein targeted to the cytoplasmic face of the plasma membrane we considered that a direct interaction between Nef and CD4 might play a role in down-modulation. Here we demonstrate that a baculovirus-expressed Nef-GST fusion protein interacts specifically with CD4. This interaction requires co-expression in the same cell and is dependent on Nef myristoylation. The site of Nef interaction maps to the cytoplasmic domain of CD4, as a deletion mutant lacking this domain fails to interact with Nef. This observation sheds new light on the biochemical function of Nef and offers new opportunities for the future development of HIV chemotherapy.
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PMID:Myristoylation-dependent binding of HIV-1 Nef to CD4. 805 54

A combination of saturation and site-directed mutagenesis was utilized to disrupt the alpha 2 domain disulfide bridge of HLA-A*0201. Mutation of cysteine 101 to a serine (C101S) or of cysteine 164 to alanine (C164A) decreased the rate of maturation of the heavy chain, the total amount of mature heavy chain within the cell, and the level of surface expression. Cells expressing these genes and loaded with a synthetic peptide derived from the influenza A matrix protein (58-66) were recognized poorly by HLA-A*0201-restricted, peptide-specific CTLs. Cells expressing mutant HLA-A*0201 loaded with a synthetic peptide derived from the HIV-1 pol protein (476-484) were not recognized by pol IV-9-specific CTLs. Mutant C164A cells infected with influenza virus were partially recognized by influenza matrix peptide-specific CTLs, while C101S cells were not lysed. Surprisingly, endogenous peptide loading of cells expressing mutant HLA-A*0201 using a minigene coding for either the influenza A matrix peptide 58-66, or HIV-1 pol peptide 476-484, resulted in efficient CTL recognition. This suggests different structural constraints for peptide binding in the endoplasmic reticulum during biosynthesis and for binding to exported molecules on the cells surface.
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PMID:Mutation of the alpha 2 domain disulfide bridge of the class I molecule HLA-A*0201. Effect on maturation and peptide presentation. 807 Nov 1

The human immunodeficiency virus type 1 (HIV-1) encoded Vpu is a small integral membrane phosphoprotein that functions in the enhancement of viral particle release and has more recently been shown to cause degradation of CD4 at the endoplasmic reticulum. We have demonstrated earlier that Vpu is phosphorylated by the ubiquitous casein kinase-2 (CK-2) in HIV-1 infected cells. The phosphoacceptor sites targeted by CK-2 in Vpu, however, have not been demonstrated and it was unclear whether Vpu was phosphorylated at one or more of its four serine residues. In this study we characterized the CK-2 phosphoacceptor sites in Vpu using recombinant CK-2 for in vitro phosphorylation of recombinant Vpu protein as well as synthetic peptides of Vpu. Phosphorylation of both Ser52 and Ser56 was demonstrated by in vitro phosphorylation using three 54-residue peptides comprising the entire hydrophilic part of Vpu and containing single serine to asparagine transitions in either position 52 or 56. The Km values of CK-2 to these peptides were established, revealing a preferential phosphorylation of Ser56. The Km values are: Ser56 = 31 microM; Ser 52 = 156 microM; wild type = 27 microM. In addition, we studied phosphorylation of Vpu by endogenous CK-2 following in vitro translation in rabbit reticulocyte lysate of wild-type Vpu or a mutant, Vpum2/6, carrying serine to asparagine changes at amino acid positions 52 and 56. The in vivo phosphorylation of Vpu was studied in transiently transfected human embryonic kidney (293) cells. In this system, the mutant Vpum2/6 was not phosphorylated, indicating that the seryl residues of Vpu at amino acid positions 52 and 56, but not those at positions 23 and 61, are phosphorylated by CK-2. The two CK-2 phosphorylation sites are conserved in all known Vpu sequences and represent the consensus Ser52GlyAsn(Glu/Asp)Ser(Glu/Asp)Gly(Glu/Asp)59. Prediction of the secondary structure revealed a conserved alpha-helix-turn-alpha-helix motif for the hydrophilic C-terminal part of Vpu. A structural model for Vpu is proposed in which the membrane anchor precedes a region comprising two amphipathic alpha-helices of opposed polarity, joined by a strongly acidic turn that protrudes into the cytoplasm and contains the CK-2 phosphorylation sites. Possible functional and structural homologies of Vpu to the membrane channel-forming M2 protein of influenza A viruses are discussed.
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PMID:The human immunodeficiency virus type 1 encoded Vpu protein is phosphorylated by casein kinase-2 (CK-2) at positions Ser52 and Ser56 within a predicted alpha-helix-turn-alpha-helix-motif. 810 1

We have purified a serine proteinase from the membrane of U-937 cells that was inhibited in a tight-binding manner by recombinant gp120 and by peptides mimicking the V3 loop of gp120 [(1993) FEBS Lett. 317, 167-172]. This proteinase has now been characterized, both structurally and functionally. It has a dual trypsin- and chymotrypsin-like specificity, and N-terminal sequence analysis of the first 32 residues indicates complete identity with leukocyte cathepsin G. Cathepsin G-like material was located at the surface of U-937 cells using a monoclonal antibody directed against leukocyte cathepsin G, and polyclonal anti-cathepsin G antibodies precipitated the purified proteinase. However, the U-937 enzyme differs slightly from commercial leukocyte cathepsin G in its apparent M(r) because of different glycosylation. No other protein structurally related to cathepsin G was found upon screening a U-937 cDNA library using several oligonucleotide probes constructed from the membrane proteinase N-terminal amino acid sequence. The possible interaction of a cathepsin G-like proteinase at the surface of U-937 cells with the V3 loop of HIV-1 gp120 is discussed.
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PMID:Identification of the U-937 membrane-associated proteinase interacting with the V3 loop of HIV-1 gp120 as cathepsin G. 819 6

HIV gp120 is specifically cleaved at a single site in the V3 loop between Arg315 and Ala316 by thrombin. Previous observations by others have indicated that binding to CD4 enhances the rate of V3 loop cleavage, and that this cleavage is a prerequisite for HIV infection. Other observations also suggest that the cleavage site is in a type II beta-turn centered at Pro313-Gly314. However, our docking experiments indicate that this conformation cannot dock to thrombin and other trypsin-like serine proteases. Thus, based on the thrombin-bound conformation of peptide substrates, we propose that CD4 binding, at a site remote from the V3 loop, induces and stabilizes a trans to cis isomerization of the highly conserved residue Pro313, and that this conformational shift is a prerequisite for cleavage by a 'thrombin-like' cellular protease and subsequent infection.
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PMID:Conformational rearrangements required of the V3 loop of HIV-1 gp120 for proteolytic cleavage and infection. 827 10

The V3 loop of the HIV (human immunodeficiency virus)-1 envelope glycoprotein gp120 likely plays a role in HIV-1 infectivity. Although the amino acid sequence of the V3 loop is hypervariable, it contains a conserved region, Gly-Pro-Gly-Arg, that shows similarity to the active-site Gly-Pro-Cys-Arg sequence of inter-alpha-trypsin and trypstatin proteinase inhibitors. The purpose of the present work was to identify proteinases recognizing substrates with basic amino acids in the P1 substrate site that are present in MOLT-4 cells, a human CD4-positive T helper lymphocyte cell line, and to characterize these enzymes in terms of substrate, pH and ionic-strength preferences, size and susceptibility to various inhibitors, including 24- and 36-amino-acid-long V3 loop peptides. Extraction of MOLT-4 cells at low ionic strength solubilized nearly all of the trypsin-like activity, which was separable into five peaks of activity by chromatography on Mono-Q: Peaks 1, 2a, 2b, 3 and 4. All showed a neutral pH optimum, and all except Peak 4 showed optimal activity at high ionic strength. Peak 1 preferred Tos-Gly-Pro-Arg, p-nitroanilide (-pNA) substrate; Peaks 2-4 preferred benzyloxycarbonyl-Val-Leu-Gly-Arg-pNA. Peak 1, a zinc-dependent enzyme with serine and histidine in the active site, exhibited an M(r) of 75,000 on Superose 12 and was poorly inhibited by V3 loop peptides. Peak 2 contained two overlapping peaks, called 2a and 2b, that exhibited properties of zinc-dependent metalloproteinases. Gel filtration of Peak 2 activities revealed a major peak of activity at 81 kDa and a shoulder centred at 240 kDa. Each was modestly inhibited by V3 loop peptides. Peak 3, a zinc-dependent proteinase, exhibited a molecular mass of 100 kDa by gel filtration and was particularly sensitive to inhibition by V3 loop peptides. Peak 4 exhibited a molecular mass of 1100 kDa by gel filtration and was not inhibited by V3 loop peptides. None of these enzymes could be classified as mast-cell tryptase, and material in MOLT-4 cells cross-reactive with anti-(human tryptase) antibodies was not detected. Whether any of the MOLT-4 proteinases described in this study play a role in HIV-1 infectivity remains to be examined.
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PMID:Separation and partial characterization of proteinases with substrate specificity for basic amino acids from human MOLT-4 T lymphocytes: identification of those inhibited by variable-loop-V3 peptides of HIV-1 (human immunodeficiency virus-1) envelope glycoprotein. 831 3


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