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O Mihalache

Publications and source records attributed to O Mihalache.

11 recordsLinked to original sources
PubMed2000

ATPase cycle controls the conformation of an archaeal chaperonin as visualized by cryo-electron microscopy.

Chaperonins are double-ring protein folding machines fueled by ATP binding and hydrolysis. Conformational rearrangements upon ATPase cycling of the group I chaperonins, typified by the Escherichia coli GroEL/GroES system, have been thoroughly investigated by cryo-electron microscopy and X-ray crystallography. For archaeal group II chaperonins, however, these methods have so far failed to provide a correlation between the structural and the functional states. Here, we show that the conformation of the native alphabeta-thermosome of Thermoplasma acidophilum in vitrified ice is strictly regulated by adenine nucleotides.

Adenosine Triphosphatases↗
PubMed2000

ATPase cycle of an archaeal chaperonin.

Recent structural data imply differences in allosteric behavior of the group I chaperonins, typified by GroEL from Escherichia coli, and the group II chaperonins, which comprise archaeal thermosome and eukaryotic TRiC/CCT. Therefore, this study addresses the mechanism of interaction of adenine nucleotides with recombinant alpha-only and native alphabeta-thermosomes from Thermoplasma acidophilum, which also enables us to analyze the role of the heterooligomeric composition of the natural thermosome. Although all subunits of the alpha-only thermosome seem to bind nucleotides tightly and independently, the native chaperonin has two different classes of ATP-binding sites. Furthermore, for the alpha-only thermosome, the steady-state ATPase rate is determined by the cleavage reaction itself, whereas, for the alphabeta-thermosome, the rate-limiting step is associated with a post-hydrolysis isomerisation into a non-covalent ADP*P(i) species prior to the release of the gamma-phosphate group. After half-saturation with ATP, a negative cooperativity in hydrolysis is observed for both thermosomes. The effect of Mg(2+) and K(+) nucleotide cycling is documented. We conclude that archaeal chaperonins have unique allosteric properties and discuss them in the light of the mechanism established for the group I chaperonins.

Adenosine Diphosphate↗
PubMed1992

Stage-specific tyrosine phosphorylation of actin in Dictyostelium discoideum cells.

A 45 kDa protein in Dictyostelium discoideum cells that was recognized by a phosphotyrosine-specific antibody was identified by its binding activity to DNase I and its 2D-electrophoretic behavior as actin. The reactivity of actin with the antibody was transiently enhanced for about 30 minutes shortly after starving cells were reintroduced into nutrient medium. This effect indicates a modification of actin that is regulated under physiological conditions. A similar effect was obtained when growing cells were treated with phenylarsine oxide (PAO), an inhibitor of phosphotyrosine phosphatases. This effect was reversed and the cells fully recovered upon addition of the PAO antagonist 2,3-dimercaptopropanol. Starved cells did not show this enhancement of antibody labelling, which indicates that the response to PAO depends on the developmental stage. Phosphorylated amino acid residues were identified after in vivo labelling with [32P]phosphate in the presence of PAO. Part of the radioactivity in the actin band was recovered as phosphotyrosine, another part as phosphoserine. PAO caused the cells to form elongated blebs, to round up and finally to become immobilized. Fluorescence labelling with phalloidin of cells that were fixed at different times of PAO treatment revealed a progressive decrease in the staining for actin filaments and showed that these alterations in cytoskeleton organization were readily reversible, in accordance with the reversal of tyrosine phosphorylation at actin.

Actins↗
PubMed1990

Phosphotyrosine-containing proteins in Dictyostelium discoideum.

Phosphotyrosine-containing proteins in Dictyostelium discoideum were detected by immunoblot analysis and immunoprecipitation using a monoclonal anti-phosphotyrosine antibody. The iodinated antibody recognized on bots a cluster of 205-220 kDa polypeptides and bands of 107 and 60 kDa. The 107 and 60 kDa polypeptides and, in addition, a 82 kDa one became phosphorylated on tyrosine when the immunoprecipitate was incubated with [gamma-32P]ATP. In preparations from differentiating cells the intensity of the label was increased in the 60 kDa band and decreased in the 107 and 205-220 kDa bands.

Antibodies, Monoclonal↗
PubMed1985

Some physico-chemical and biological properties of egg-Sendai virus with altered haemagglutinin-neuraminidase protein.

Some physico-chemical and biological properties of egg-cultivated Sendai (egg-Sendai) virus particles with altered haemagglutinin-neuraminidase (HN) protein were studied. These particles were obtained accidentally from purified egg-Sendai virus stored at +4 degrees C. Egg-Sendai with altered HN protein was not infectious for cultured cells, but could still infect embryonated eggs. Though egg-Sendai virus with altered HN protein and glycoproteins had no haemagglutination activity, it unexpectedly possessed a relatively high neuraminidase (NA) activity representing about 70% of the activity of normal particles. Since polyacrylamide gel and rocket immunoelectrophoresis indicated that the altered particles contained only F protein, possibly the native HN was converted into a molecule of the same molecular mass as F protein.

Antigens, Viral↗
PubMedDate not supplied

Preliminary data on the encapsulation of biologically active materials in liposomes.

Multilamellar and unilamellar phospholipid liposomes were prepared and investigated as regards their properties and the capacity of encapsulating biologically active materials, such as CrO4-(2-)ions, basic dyes, proteins, DNA, as well as Sendai virus particles. The efficiency of encapsulation ranged from 10% for CrO4-(2-)ions to about 80% for toluidine blue; it was found to depend not only on the type of encapsulated material, but also on the method used for liposome preparation and on liposome composition.

Animals↗
PubMedDate not supplied

Polypeptide changes in Sendai virus-infected cells.

The appearance of virus-specific proteins in Sendai virus-infected chick embryo fibroblasts and chorioallantoic membrane cells was studied by high resolution SDS-polyacrylamide gel electrophoresis. All the structural Sendai virus polypeptides, as well as the nonstructural virus polypeptide termed B could be identified in the total lysates of infected cells. Only the structural virus polypeptides NP, P and M were found in the ribosome fraction of virus-infected cells; these additional polypeptides were removed from the ribosome surface by washing the 1 M NH4Cl.

Animals↗
PubMedDate not supplied

The effect of violamycin BI on different biological systems. Note I. The action of violamycin BI on cell cultures infected or not with herpes simplex virus type 1.

The effect of violamycin BI (VBI) was investigated in different cell substrates, infected or not with herpes simplex virus type 1 (HSV-1), strains VR3 and Rapp-1. The cytotoxic dose of VBI was established in calf kidney and human embryo cell cultures. Low drug concentrations induced moderate cytotoxic changes, allowing the study of the cells for 4-6 days. The action of VBI on HSV-1 was evident mostly in the early phases of the virus multiplication cycle. The antiviral effect of VBI was due both to the direct action of the drug on HSV and to its interaction with the nucleic acids of the host cells supporting HSV multiplication in their nuclei.

Aminoglycosides↗
PubMedDate not supplied

EPR and Mössbauer spectroscopy investigations on the metal ion contents of Sendai virus components.

EPR and Mössbauer spectroscopy indicate that Sendai virus contains iron ions in paramagnetic states. Spectral data show that the iron ions are in an oxidized form (Fe3+), having low and high spin states (S = 1/2 and S = 5/2). On enrichment of Sendai virus with 57Fe, the concentration of Fe3+ ions substantially increases in the virus preparations. The Fe3+ ions in the high spin state appear to be tightly bound to the virus components; they are not significantly removed by dialysis. The five main proteins separated by SDS gel electrophoresis from 57Fe-enriched Sendai virus contain the signal corresponding to the presence of Fe3+ ions in the high spin state. The concentration of Fe3+ ions is, however, about five times higher in the HN polypeptide than in the other four components. It is suggested that Fe3+ (5/2) ions might be a structural component of the Sendai virus HN polypeptide.

Electron Spin Resonance Spectroscopy↗
PubMedDate not supplied

Effect of biologically active compounds (anthracyclines and ethidium bromide) on some membrane-mediated processes in the course of viral infection. Investigations on a prokaryotic (bacteriophage-bacterium) system.

Anthracycline antibiotics--violamycin B1 and adriamycin--have an obvious effect on the efficiency of phage lambda L47.1 DNA transfection into E. coli Q358 cells. Treatment with anthracyclines of either phage DNA or bacterial cells results in a marked decrease in the number of transfectants per microgram DNA. On the other hand, adsorption of phage lambda gt WES to E. coli LE392 is considerably modified by exposure to anthracyclines of either the phage or the host cells.

Adsorption↗