Application of kinetic-based biospecific affinity chromatographic systems to ATP-dependent enzymes: studies with yeast hexokinase

This study is concerned with the development of kinetic-based bioaffinity chromatographic systems for purification of ATP-dependent kinases, with a particular focus on the allosteric yeast hexokinase enzyme (EC 2.7.1.1). Synthesis and characterization of highly substituted N(6)-linked and S(6)-linked immobilized ATP derivatives are described using a rapid solid-phase modular approach. Evaluation of the new immobilized ATP derivatives has been carried out using model chromatographic studies with yeast hexokinase, employing specific substrate analogues (N-acetyl-D-glucosamine and suramin) to promote biospecific adsorption, in the presence and absence of citrate (a so-called allosteric activator of hexokinase activity). In this paper, successful bioaffinity chromatography systems were developed for yeast hexokinase and, as a result, interesting binding and catalytic properties of the enzyme were highlighted and explored. The overall results confirm the potential for extrapolation of the kinetic locking-on tactic, a general kinetic-based bioaffinity approach already developed for the NAD(P)(+)-dependent dehydrogenases, to ATP/ADP-dependent enzymes. However, in view of the enhancement of the intrinsic ATPase activity of hexokinase with glucosamine derivatives, and the coincidental hydrolysis of immobilized ATP to immobilized ADP, future developments necessary to support adaptation of the approach to ATP-dependent enzymes are discussed.     

Phenotype and regulation of persistent intracerebral T cells in murine Toxoplasma encephalitis

Toxoplasma gondii is a parasite causing asymptomatic, persistent encephalitis. Protective CD4 and CD8 T cells are recruited to and accumulate in the brain in acute Toxoplasma encephalitis (TE), with slowly decreasing numbers in chronic TE. It is unclear how the size of the intracerebral T cell pool is regulated. Conceivably, permanent recruitment, proliferation, and apoptosis may be involved. We observed that in murine TE recruitment of T cells to the brain was terminated in chronic TE. In vivo 5-bromo-2'-deoxyuridine incorporation and in vitro T cell proliferation experiments revealed that intracerebral T cells did not proliferate, which was explained by the expression of the cell cycle inhibitors p21(Waf/cip1) and p27(Kip1) and the inhibitory activity of intracerebral F4/80(+) cells. TUNEL staining detected apoptotic T cells at low frequency corresponding to an increased expression of the anti-apoptotic molecules Bcl-2 and Bcl-x(L) and a reduced expression of the pro-apoptotic molecules Bad, Bax, and Fas ligand in CD4 and CD8 T cells. During progression from acute to chronic TE, both CD4 and CD8 T cells down-regulated CD45RB expression and expressed a differential pattern of cytokines. From these experiments it is concluded that the number of intracerebral T cells increases by recruitment of T cells during acute infection, whereas proliferation of intracerebral T cells does not play a role. In chronic TE, T cell recruitment is terminated, the phenotype of intracerebral T cells changes, and their number is gradually downsized by low level apoptosis, which, however, does not completely resolve the T cell infiltrates.     

The ubiquitous chromatin protein DEK alters the structure of DNA by introducing positive supercoils

We have investigated the molecular mechanism by which the proto-oncogene protein DEK, an abundant chromatin-associated protein, changes the topology of DNA in chromatin in vitro. Band-shift assays and electron microscopy revealed that DEK induces both intra- and intermolecular interactions between DNA molecules. Binding of the DEK protein introduces constrained positive supercoils both into protein-free DNA and into DNA in chromatin. The induced change in topology is reversible after removal of the DEK protein. As shown by sedimentation analysis and electron microscopy, the DEK-induced positive supercoiling causes distinct structural changes of DNA and chromatin. The observed direct effects of DEK on chromatin folding help to understand the function that this major chromatin protein performs in the nucleus.     

Tracking the immunoregulatory mechanisms active during allograft tolerance

Immunoregulatory mechanisms dependent on regulatory CD4+ T cells are believed to be critical in the maintenance of peripheral tolerance to allografts. However, a detailed characterization of the effects of these regulatory T cells has been hampered by the absence of a simple means to track and study them. In this work we provide evidence that in a murine model of islet transplantation the interactions between alloaggressive and regulatory T cells can be studied in vitro and in vivo at the single-cell level. The observations made in both an in vitro coculture system and an in vivo CFSE-based adoptive transfer model indicate that lymphocytes from tolerant allograft recipients 1) proliferate weakly to donor strain allogeneic cells but vigorously to third-party strain cells; and 2) suppress the proliferation of naive syngeneic CD4+ and CD8+ T cells to donor tissue in a cell dose- and Ag-specific manner. These effects depend on the presence of CD4+CD25+ T cells and are neutralized by anti-CTLA4 mAb or rIL-2. The principal effect of anti-CTLA4 is directed against the naive, not regulatory, T cell population. These results can be replicated in vivo by transferring lymphocyte populations into transplant recipients, proving that the graft-protecting actions of regulatory T cells are blunted by a rise in the number of allodestructive T cells (pool size model) and depend on the presence of CD4+CD25+ T cells and the integrity of the CTLA4/B7 pathway.     

Hydroxylated 2-amino-3H-phenoxazin-3-one derivatives as products of 2-hydroxy-1,4-benzoxazin-3-one (HBOA) biotransformation by Chaetosphaeria sp., an endophytic fungus from Aphelandra tetragona

The biotransformation of the phytoanticipin HBOA and its major degradation metabolites 2-hydroxy-N-(2-hydroxyphenyl)acetamide (7) and N-(2-hydroxyphenyl)acetamide (8) by Chaetosphaeria sp., an endophytic fungus isolated from Aphelandra tetragona, was studied. Three new metabolites could be identified as 2-amino-7-hydroxy-3H-phenoxazin-3-one (12), 2-acetylamino-7-hydroxy-3H-phenoxazin-3-one (13) and 7-hydroxy-2-(2-hydroxyacetyl)-amino-3H-phenoxazin-3-one (14). Structure elucidation of 12 and 13 was performed by MS, 1H, 13C NMR and 2D NMR techniques and confirmed by chemical transformation.     

Evidence for the presence and activity of a complete antioxidant defence system in mature sieve tubes

The phloem is the major route for the transport of solutes and nutrients from source to sink organs in plants. The functional transport phloem consists of parenchymal tissue, enucleate sieve elements, and the intimately connected companion cells. The general absence of a nucleus and functional ribosomes in sieve tubes poses problems especially for damage avoidance and repair of sieve element components. To examine how sieve tubes can remain functional during oxidative stress, we analysed phloem sap of cucumber and pumpkin plants with respect to the presence of antioxidant defence enzymes, their enzymatic activity, and activity changes after exposure to drought stress. Using 1D SDS-PAGE and nano ESI MS/MS, the presence of proteins such as cytosolic Cu/Zn superoxide dismutase, monodehydroascorbate reductase, and peroxidase could be shown. Moreover, activities for several antioxidant enzymes (superoxide dismutase, dehydroascorbate reductase, peroxidase) in phloem exudate could be demonstrated. The activity of these enzymes in phloem sap from cucumber and pumpkin plants increased in response to drought stress. The presented results together with earlier findings provide evidence supporting the presence of a complete machinery of antioxidant defence enzymes and detoxifying metabolites important for avoiding damage to essential components of the sieve elements due to oxidative stress.     

Dephosphorylation of tau protein by calcineurin triturated into neural living cells

Alzheimer disease and related dementia are characterized by the presence of hyperphosphorylated tau aggregated into filaments. The role of tau phosphorylation in the fibrillogenesis has not yet been unraveled. Therefore, it is important to know which phosphatases can dephosphorylate tau protein in vivo. The effect of recombinant purified calcineurin (CN(PP2B)) and several calcineurin mutants on tau phosphorylation was studied in two neuronal like cell lines PC12 and SH-SY5Y. The modulation of tau phosphorylation at Ser199/Ser202, Ser396/Ser404, Ser262/Ser356, and Thr181 sites was examined in these cell lines using the phosphorylation state-dependent antitau antibodies Tau 1, PHF1, 12E8, and AT270. The results have shown that CN directly dephosphorylates all of those sites of tau protein. Recombinant calcineurin introduced into cells that have previously been treated with okadaic acid and cyclosporin A, which are inhibitors of phosphatases (PP1/PP2A and PP2B), has a direct effect on the phosphorylation status on all phosphorylation sites studied. We conclude that calcineurin is (besides PP2A) a important modulator of tau phosphorylation in vivo.