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

Gag polyprotein-mediated incorporation of cellular cyclophilin A (CyPA) into virions is essential for the formation of infectious human immunodeficiency virus type 1 (HIV-1) virions. Either a point mutation in Gag (P222A) or drugs which bind CyPA decrease virion incorporation of CyPA and interfere with HIV-1 replication. We have found that lymphoid cells varied greatly in their CyPA content and that cells with high CyPA content supported the replication of P222A HIV-1 Gag mutants. These experiments demonstrated that a higher cellular CyPA content of some cells was able to compensate for the decreased binding affinity of P222A mutant Gag for CyPA, allowing virus replication to occur.
 ...
PMID:Cells with high cyclophilin A content support replication of human immunodeficiency virus type 1 Gag mutants with decreased ability to incorporate cyclophilin A. 942 Feb 28

Retroviruses are produced as immature particles containing structural polyproteins, which are subsequently cleaved by the viral proteinase (PR). Extracellular maturation leads to condensation of the spherical core to a capsid shell formed by the capsid (CA) protein, which encases the genomic RNA complexed with nucleocapsid (NC) proteins. CA and NC are separated by a short spacer peptide (spacer peptide 1 [SP1]) on the human immunodeficiency virus type 1 (HIV-1) Gag polyprotein and released by sequential PR-mediated cleavages. To assess the role of individual cleavages in maturation, we constructed point mutations abolishing cleavage at these sites, either alone or in combination. When all three sites between CA and NC were mutated, immature particles containing stable CA-NC were observed, with no apparent effect on other cleavages. Delayed maturation with irregular morphology of the ribonucleoprotein core was observed when cleavage of SP1 from NC was prevented. Blocking the release of SP1 from CA, on the other hand, yielded normal condensation of the ribonucleoprotein core but prevented capsid condensation. A thin, electron-dense layer near the viral membrane was observed in this case, and mutant capsids were significantly less stable against detergent treatment than wild-type HIV-1. We suggest that HIV maturation is a sequential process controlled by the rate of cleavage at individual sites. Initial rapid cleavage at the C terminus of SP1 releases the RNA-binding NC protein and leads to condensation of the ribonucleoprotein core. Subsequently, CA is separated from the membrane by cleavage between the matrix protein and CA, and late release of SP1 from CA is required for capsid condensation.
 ...
PMID:Sequential steps in human immunodeficiency virus particle maturation revealed by alterations of individual Gag polyprotein cleavage sites. 952 4

Host proteins are incorporated into retroviral virions during assembly and budding. We have examined three retroviruses, human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency virus (SIV), and Moloney murine leukemia virus (Mo-MuLV), for the presence of ubiquitin inside each of these virions. After a protease treatment to remove exterior viral as well as contaminating cellular proteins, the proteins remaining inside the virion were analyzed. The results presented here show that all three virions incorporate ubiquitin molecules at approximately 10% of the level of Gag found in virions. In addition to free ubiquitin, covalent ubiquitin-Gag complexes were detected, isolated, and characterized from all three viruses. Our immunoblot and protein sequencing results on treated virions showed that approximately 2% of either HIV-1 or SIV p6Gag was covalently attached to a single ubiquitin molecule inside the respective virions and that approximately 2 to 5% of the p12Gag in Mo-MuLV virions was monoubiquitinated. These results show that ubiquitination of Gag is conserved among these retroviruses and occurs in the p6Gag portion of the Gag polyprotein, a region that is likely to be involved in assembly and budding.
 ...
PMID:Ubiquitin is covalently attached to the p6Gag proteins of human immunodeficiency virus type 1 and simian immunodeficiency virus and to the p12Gag protein of Moloney murine leukemia virus. 952 17

The matrix protein of human immunodeficiency virus type 1 (HIV-1) has been reported to play a crucial role in the targeting of the Gag polyprotein precursor to the plasma membrane and in the incorporation of viral envelope glycoproteins into budding virions. In this report, we present evidence that mutation of a highly conserved Leu at matrix amino acid 20 blocks or markedly delays virus replication in a range of cell types, including T-cell lines, primary human peripheral blood mononuclear cells, and monocyte-derived macrophages. These mutations do not impair virus assembly and release, RNA encapsidation, or envelope glycoprotein incorporation into virions but rather cause significant defects in an early step in the virus life cycle, as measured by single-cycle infectivity assays and the analysis of viral DNA synthesis early postinfection. This infectivity defect is independent of the type of envelope glycoprotein carried on mutant virions; similar results are obtained in pseudotyping experiments using wild-type or truncated HIV-1 envelope glycoproteins, the amphotropic murine leukemia virus envelope, or the vesicular stomatitis G protein. Intriguingly, matrix residue 20 mutations also increase the apparent binding of Gag to membrane, accelerate the kinetics of Gag processing, and induce defects in endogenous reverse transcriptase activity without affecting virion density or morphology. These results help elucidate the function of matrix in HIV-1 replication.
 ...
PMID:Role of matrix in an early postentry step in the human immunodeficiency virus type 1 life cycle. 955 1

Incorporation of Vpx into human immunodeficiency virus type 2 (HIV-2) virus-like particles is mediated by the Gag polyprotein. We have identified residues 15 to 40 of Gag p6 and residues 73 to 89 of Vpx as being necessary for virion incorporation. In addition, we show enhanced in vitro binding of Vpx to a chimeric HIV-1/HIV-2 Gag construct containing residues 2 to 49 of HIV-2 p6 and demonstrate that the presence of residues 73 to 89 of Vpx allows for in vitro binding to HIV-2 Gag.
 ...
PMID:Human immunodeficiency virus type 2 Vpx-Gag interaction. 957 3

A recombinant replication-incompetent herpes simplex virus vector (vd120/Gag) that expressed the human immunodeficiency virus 1 gag gene and part of the pol gene that encodes the HIV-1 protease was constructed. Examination of cells infected with vd120/Gag revealed the presence of the Gag polyprotein Pr55gag by 12 h post-infection, as well as abundant levels of the proteolytically processed 24-kDa capsid protein. Analysis of vector-infected cells and culture supernatant indicated that the majority of the 24-kDa protein remained cell-associated. Although the HIV-1 Gag polyprotein was produced in vd120/Gag-infected cells, there was no evidence of HIV virus-like particle production upon examination of vector-infected cells by transmission electron microscopy.
 ...
PMID:Expression of the human immunodeficiency virus gag gene products by a replication-incompetent herpes simplex virus vector. 966 69

A series of mutations, first identified in protease inhibitor-resistant HIV-1 viral isolates, were introduced into HIV-1 PR as individual substitutions. Mutants containing R8K, V32I, V82T, I84V, G48V/L90M, or V82T/I84V substitutions were analyzed for differences in substrate preference and catalytic efficiency using a set of single amino acid substituted HIV-1 CA-NCa cleavage site peptides. All mutants exhibited wild-type preference for large hydrophobic residues, especially Phe, in the P1' substrate position. Only the R8K and V32I mutants showed significant differences in subsite selection compared to wild-type enzyme. In a parallel study, the individual mutations R10K, L12V, I44V, A60M, I71V, and I108V were introduced into RSV PR. These amino acid positions are structurally equivalent to Arg8, Leu10, Val32, Met46, Ile54, and Ile84 in HIV-1 PR, respectively, which mutate in drug-resistance. The RSV R10K substitution significantly altered substrate specificity and catalytic rate, compared to wild-type, in a manner similar to that of the HIV-1 R8K mutant. Crystal structures of the RSV PR R10K, I44V, I71V, and Il08V mutant enzymes presented here indicate that each of these substitutions has little effect on the overall structure of the respective enzymes. Taken together, these data provide an explanation for the reported in vivo predilection for selection of large hydrophobic residues in the P1' substrate position of second locus mutations in the Gag polyprotein PR cleavage sites. The data also suggest that the selection of resistant enzymes is not simply limited to loss of binding to inhibitor but affects other steps in proteolysis.
 ...
PMID:Drug-resistant HIV-1 proteases identify enzyme residues important for substrate selection and catalytic rate. 975 73

The p6(Gag) protein of human immunodeficiency virus type 1 (HIV-1) is produced as the carboxyl-terminal sequence within the Gag polyprotein. The amino acid composition of this protein is high in hydrophilic and polar residues except for a patch of relatively hydrophobic amino acids found in the carboxyl-terminal 16 amino acids. Internal cleavage of p6(Gag) between Y36 and P37, apparently by the HIV-1 protease, removes this hydrophobic tail region from approximately 30% of the mature p6(Gag) proteins in HIV-1MN. To investigate the importance of this cleavage and the hydrophobic nature of this portion of p6(Gag), site-directed mutations were made at the minor protease cleavage site and within the hydrophobic tail. The results showed that all of the single-amino-acid-replacement mutants exhibited either reduced or undetectable cleavage at the site yet almost all were nearly as infectious as wild-type virus, demonstrating that processing at this site is not important for viral replication. However, one exception, Y36F, was 300-fold as infectious the wild type. In contrast to the single-substitution mutants, a virus with two substitutions in this region of p6(Gag), Y36S-L41P, could not infect susceptible cells. Protein analysis showed that while the processing of the Gag precursor was normal, the double mutant did not incorporate Env into virus particles. This mutant could be complemented with surface glycoproteins from vesicular stomatitis virus and murine leukemia virus, showing that the inability to incorporate Env was the lethal defect for the Y36S-L41P virus. However, this mutant was not rescued by an HIV-1 Env with a truncated gp41(TM) cytoplasmic domain, showing that it is phenotypically different from the previously described MA mutants that do not incorporate their full-length Env proteins. Cotransfection experiments with Y36S-L41P and wild-type proviral DNAs revealed that the mutant Gag dominantly blocked the incorporation of Env by wild-type Gag. These results show that the Y36S-L41P p6(Gag) mutation dramatically blocks the incorporation of HIV-1 Env, presumably acting late in assembly and early during budding.
 ...
PMID:Mutational analysis of the hydrophobic tail of the human immunodeficiency virus type 1 p6(Gag) protein produces a mutant that fails to package its envelope protein. 984 2

Recently, it was shown that actin molecules are present in human immunodeficiency virus type 1 (HIV-1) particles. We have examined the basis for incorporation and the location of actin molecules within HIV-1 and murine retrovirus particles. Our results show that the retroviral Gag polyprotein is sufficient for actin uptake. Immunolabeling studies demonstrate that actin molecules localize to a specific radial position within the immature particle, clearly displaced from the matrix domain underneath the viral membrane but in proximity to the nucleocapsid (NC) domain of the Gag polyprotein. When virus or subviral Gag particles were disrupted with nonionic detergent, actin molecules remained associated with the disrupted particles. Actin molecules remained in a stable complex with the NC cleavage product (or an NC-RNA complex) after treatment of the disrupted HIV-1 particles with recombinant HIV-1 protease. In contrast, matrix and capsid molecules were released. The same result was obtained when mature HIV-1 particles were disrupted with detergent. Taken together, these results indicate that actin molecules are associated with the NC domain of the viral polyprotein.
 ...
PMID:Actin associates with the nucleocapsid domain of the human immunodeficiency virus Gag polyprotein. 997 72

Human immunodeficiency virus type 1 (HIV-1) normally assembles into particles of 100 to 120 nm in diameter by budding through the plasma membrane of the cell. The Gag polyprotein is the only viral protein that is required for the formation of these particles. We have used an in vitro assembly system to examine the assembly properties of purified, recombinant HIV-1 Gag protein and of Gag missing the C-terminal p6 domain (Gag Deltap6). This system was used previously to show that the CA-NC fragment of HIV-1 Gag assembled into cylindrical particles. We now report that both HIV-1 Gag and Gag Deltap6 assemble into small, 25- to 30-nm-diameter spherical particles in vitro. The multimerization of Gag Deltap6 into units larger than dimers and the formation of spherical particles required nucleic acid. Removal of the nucleic acid with NaCl or nucleases resulted in the disruption of the multimerized complexes. We conclude from these results that (i) N-terminal extension of HIV-1 CA-NC to include the MA domain results in the formation of spherical, rather than cylindrical, particles; (ii) nucleic acid is required for the assembly and maintenance of HIV-1 Gag Deltap6 virus-like particles in vitro and possibly in vivo; (iii) a wide variety of RNAs or even short DNA oligonucleotides will support assembly; (iv) protein-protein interactions within the particle must be relatively weak; and (v) recombinant HIV-1 Gag Deltap6 and nucleic acid are not sufficient for the formation of normal-sized particles.
 ...
PMID:In vitro assembly properties of human immunodeficiency virus type 1 Gag protein lacking the p6 domain. 997 10


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>