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Biomedical subjects

I Törö

Publications and source records attributed to I Törö.

At least 19 recordsLinked to original sources
PubMed2001

RNA binding in an Sm core domain: X-ray structure and functional analysis of an archaeal Sm protein complex.

Eukaryotic Sm and Sm-like proteins associate with RNA to form the core domain of ribonucleoprotein particles involved in pre-mRNA splicing and other processes. Recently, putative Sm proteins of unknown function have been identified in Archaea. We show by immunoprecipitation experiments that the two Sm proteins present in Archaeoglobus fulgidus (AF-Sm1 and AF-Sm2) associate with RNase P RNA in vivo, suggesting a role in tRNA processing. The AF-Sm1 protein also interacts specifically with oligouridylate in vitro. We have solved the crystal structures of this protein and a complex with RNA. AF-Sm1 forms a seven-membered ring, with the RNA interacting inside the central cavity on one face of the doughnut-shaped complex. The bases are bound via stacking and specific hydrogen bonding contacts in pockets lined by residues highly conserved in archaeal and eukaryotic Sm proteins, while the phosphates remain solvent accessible. A comparison with the structures of human Sm protein dimers reveals closely related monomer folds and intersubunit contacts, indicating that the architecture of the Sm core domain and RNA binding have been conserved during evolution.

Archaeal Proteins↗
PubMed2001

Conformational flexibility in T4 endonuclease VII revealed by crystallography: implications for substrate binding and cleavage.

The structure of the N62D mutant of the junction-resolving endonuclease VII (EndoVII) from phage T4 has been refined at 1.3 A, and a second wild-type crystal form solved and refined at 2.8 A resolution. Comparison of the mutant with the wild-type protein structure in two different crystal environments reveals considerable conformational flexibility at the dimer level affecting the substrate-binding cleft, the dimerization interface and the orientation of the C-terminal domains. The opening of the DNA-binding cleft, the orientation of the C-terminal domains relative to the central dimerization domain as well as the relative positioning of helices in the dimerization interface appear to be sensitive to the crystal packing environment. The highly unexpected rearrangement within the extended hydrophobic interface does change the contact surface area but keeps the number of hydrophobic contacts about the same and will therefore not require significant energy input. The conformational flexibility most likely is of functional significance for the broad substrate specificity of EndoVII. Binding of sulphate ions in the mutant structure and their positions relative to the active-site metal ions and residues known to be essential for catalysis allows us to propose a possible catalytic mechanism. A comparison with the active-site geometries of other magnesium-dependent nucleases, among them the homing endonuclease I-PpoI and Serratia endonuclease, shows common features, suggesting related catalytic mechanisms.

Amino Acid Substitution↗
PubMed1999

A thermodynamic study of the 434-repressor N-terminal domain and of its covalently linked dimers.

The isolated N-terminal 1-69 domain of the 434-phage repressor, R69, and its covalently linked (head-to-tail and tail-to-tail) dimers have been studied by differential scanning microcalorimetry (DSC) and CD. At neutral solvent conditions the R69 domain maintains its native structure, both in isolated form and within the dimers. The stability of the domain depends highly upon pH within the acidic range, thus at pH 2 and low ionic strength R69 is already partially unfolded at room temperature. The thermodynamic parameters of unfolding calculated from the DSC data are typical for small globular proteins. At neutral pH and moderate ionic strength, the domains of the dimers behave as two independent units with unfolding parameters similar to those of the isolated domain, which means that linking two R69 domains, either by a long peptide linker or by a designed C-terminal disulfide bridge, does not induce any cooperation between them.

Calorimetry, Differential Scanning↗
PubMed1997

Single-chain repressors containing engineered DNA-binding domains of the phage 434 repressor recognize symmetric or asymmetric DNA operators.

Single-chain (sc) DNA-binding proteins containing covalently dimerized N-terminal domains of the bacteriophage 434 repressor cI have been constructed. The DNA-binding domains (amino acid residues 1 to 69) were connected in a head-to-tail arrangement with a part of the natural linker sequence that connects the N and C-terminal domains of the intact repressor. Compared to the isolated N-terminal DNA-binding domain, the sc molecule showed at least 100-fold higher binding affinity in vitro and a slightly stronger repression in vivo. The recognition of the symmetric O(R)1 operator sequence by this sc homodimer was indistinguishable from that of the naturally dimerized repressor in terms of binding affinity, DNase I protection pattern and in vivo repressor function. Using the new, sc framework, mutant proteins with altered DNA-binding specificity have also been constructed. Substitution of the DNA-contacting amino acid residues of the recognition helix in one of the domains with the corresponding residues of the Salmonella phage P22 repressor c2 resulted in a sc heterodimer of altered specificity. This new heterodimeric molecule recognized an asymmetric, artificial 434-P22 chimeric operator with high affinity. Similar substitutions in both 434 domains have led to a new sc homodimer which showed high affinity binding to a natural, symmetric P22 operator. These findings, supported by both in vitro and in vivo experiments, show that the sc architecture allows for the introduction of independent changes in the binding domains and suggest that this new protein framework could be used to generate new specificities in protein-DNA interaction.

Amino Acid Sequence↗
PubMed1988

Formation of lymphoepithelial tissue in the sheep's palatine tonsil.

Formation of lymphoepithelial tissue was studied in 1-, 10- and 21-day-old sheep. From each of the animals one of the tonsils was fixed in 4% glutaraldehyde for light- and electron microscopy while the other was frozen in liquid nitrogen for immunohistochemistry. These examinations revealed sequential histological events during the formation of reticular epithelium. (i) Appearance of a distinct epithelial cell indicates the initiation of the reticulation. The electron density of these epithelial cells is much lower than that of the common keratinocytes but the presence of cytoplasmic tonofibrils and desmosomes provides evidence that they are of epithelial origin. They may represent the precursors of M cells. Their appearance may be followed by expression of Ia+ molecules on the surrounding keratinocytes showed by isolated Ia+ areas in the epithelium. (ii) In the mesenchyme underneath the Ia+ epithelial areas, Ia+ dendritic-like cells emerge which immigrate through the basement membrane into the epithelium establishing a provisional dendro-epithelial tissue. In this stage of the reticular epithelium's formation large Ia+ areas are shown by immunostaining, which include the epithelium and mesenchyme. The origin of the Ia+ dendritic-like cells is uncertain but their distribution and dense accumulation underneath the epithelium suggest that they are transformed tonsillar mesenchymal cells. Similar cell transformation of mesenchymal cells takes place in the bursa of Fabricius prior to development of lymphoepithelial tissue. (iii) The M cell precursors together with the Ia+ dendritic-like cells adapt the epithelium to be suitable for receiving a large number of lymphoid cells. Immigration of the lymphoid cells into the epithelium transforms the dendro-epithelial tissue to a real lymphoepithelial one.

Animals↗
PubMed1986

Bursal development in normal and testosterone-treated chick embryos.

The development of the bursa of Fabricius was studied in normal and testosterone-treated embryos. The bursal anlage appears on the 5th day of incubation as an outgrowth of the dorso-caudal wall of the cloaca. By Day 7, the bursal lumen is present and separated from the anal invagination by a thin epithelial membrane. Shortly after this developmental state, the epithelial membrane disappears and the bursal lumen freely communicates with the amniotic cavity. The remnant of the bursal anlage forms the ventral wall of the anal invagination that is actually the bursal duct. Disappearance of the remnant of the bursal anlage, which takes place after the 16th day of incubation, allows the bursa to join the cloaca. Bursal folds appear on the 10th day of incubation. Mesenchymal cells then differentiate into dark and light cells. The dark cells, between 11 and 14 days of incubation, mobilize in the mesenchymal network and assemble in small groups under the epithelial rudiment of the folds. They, then, enter the epithelium where they induce bud formation. During the assemblage of dark cells beneath the epithelium and their emigration into the epithelium, they acquire cytoplasmic granules that resemble avian secretory cells. The light cells do not associate with the epithelium. They may be the precursors of cortical reticular cells. The differentiation of dark cells is inhibited in the presence of testosterone. Therefore, the failure of bud formation and subsequent follicular formation in the bursa of testosterone-treated embryos may be attributed to the elimination of an induction signal supplied by the differentiated dark cells of the mesenchyme.

Animals↗
PubMed1985

Immunohistochemical localization of cells reacting with monoclonal antibodies directed against the interleukin-2 receptor of murine, rat and human origin.

Recently, species specific monoclonal antibodies, directed against the interleukin-2 (IL-2) receptor of murine, rat and human origin, have been produced. In this study we demonstrate with immunohistological methods that cells reacting with these antibodies are present in normal primary and secondary lymphatic organs. The cells are exclusively localized in T cell-dependent areas, and their number increased as a result of immunization.

Animals↗
PubMed1984

Rat thymocyte subpopulations: heterogeneity of the fetal calf serum dependent rosette forming cells.

We demonstrate heterogeneity within a rat thymic cortical population, the fetal calf serum dependent rosette forming cells. Approximately half of these cells are guinea pig serum sensitive. Guinea pig serum sensitive and insensitive rosette forming cells show different distribution patterns on a continuous gradient of Percoll. They contain different amounts of TdT enzyme and regenerate with different time kinetics following sublethal irradiation. These data demonstrate new aspects of heterogeneity within the rat thymic cortical population.

Animals↗
PubMed1981

Effects of cyclophosphamide on the rat's mesenteric lymph node.

A single large dose (200 mg) of cyclophosphamide (Cy) given to adult rats caused a drastic depletion of lymphocytes occurring earlier in the B dependent compartment than in the T dependent one of the lymph node cortex. The drug had a somewhat facilitating effect on the early differentiation of plasma cells (between 12 and 24 h) which later were also depleted. By Cy administration two types of macrophage were distinguished morphologically and topographically in the lymph nodes. Cy effect the endothelial cells lining the blood vessels and lymph sinuses. From day 4 to 7 Cy caused a constant flooding of red blood cells into the lymph node sinuses like in the normal rat haemolymph gland. Regeneration of the mesenteric lymph nodes occurred by a repopulation of lymphoid cells and a proliferation of other cell types. Repopulation of the B dependent compartment lagged behind that of the T dependent compartment. Regeneration of endothelial cells seemed to be one of the factors facilitating the repopulation of lymphoid cells. The distribution of T and B dependent cells in different compartments of the rat lymph node and activation of mononuclear phagocytes in Cy treated rat lymph node are discussed.

Animals↗
PubMed1980

Functional structure in lymphoepithelial cooperation.

With the help of electron microscopic investigations the morphological and functional connection of the epithelialial and lymphoid elements was examined in the lymphoepithelial organs (thymus, bursa of Fabricius, tonsils, Peyer's patches, gland of Harder). In all these organs special receptor cells were demonstrated, which may play a role in the uptake and transfer of the antigen. In the cytoplasm they all contain characteristic flattened vacuoles, with walls similar to the structure of the cell membrane. Formation of these bodies is identified with the striated bodies of micropinocytosis vermiformis and it was observed that the endocytosis start with a disintegration of the cell membrane which enters with the absorbed antigen in characteristic form into the cytoplasm of the epithel cell and induces the process of cellular immunity. Besides the function of lacrimal secretion the Harder's gland, as a lymphoepithelial organ is full of plasma cells, which constitutes the main lymphoid elements of this organ.

Animals↗
PubMed1978

Histology and ultrastructure of the the harderian glands - accessory lacrimal gland - of the chicken.

The Harderian gland is an exocrine gland located in the orbit of the chicken. In the stroma of the folds, an extreme amount of plasma cells can be observed. Electron-microscopic observations revealed that the surface epithelium over the margin of the folds is joined up to deeper epithelial cells with processes rich in tonofibrils and the space among them is filled with plasma cells. The basement membrane separating the surface epithelium from the underlying connective tissue is lacking in these areas, therefore, plasma cells are in direct contact with epithelial cells. A fine network of reticular fibrils can be found inside the folds and reticulum cell-like elements with long processes are intercalated among the plasma cells. This morphology resembles that of the lymphoepithelial organs. Based on this similarity the lymphoepithelial character and a possible immunological function of the Harderian gland is supposed.

Animals↗