Three-dimensional structure at 5 Å resolution of cytosolic aspartate transaminase from chicken heart

An X-ray study of orthorhombic crystals of cytosolic aspartate transaminase from chicken heart has been carried out at 5 Å resolution. The crystals belong to space group P2₁2₁2₁, with unit cell dimensions $\text{a = 62.7}\text{A}\text{?}\text{, b = 118.1}\text{A}\text{?}\text{, c = 124.5}\text{A}\text{?}$. The electron density map has been calculated on the basis of five heavy-atom derivatives. The model of the molecule derived from this map revealed clearly two subunits of similar structure related by a non-crystallographic dyad. The secondary structure of the protein comprises nine helical segments per subunit.The enzyme has been shown to be catalytically active in the crystal form. Removal of the coenzyme from the crystals made it possible to derive from the difference Fourier map the position of the active site in the enzyme molecule.Significant conformational changes have been observed which accompany the interconversion of intermediates of the enzymic reaction.     

Mesenchymal stem cell-based HSP70 promoter-driven VEGFA induction by resveratrol promotes angiogenesis in a mouse model

Several studies of stem cell-based gene therapy have indicated that long-lasting regeneration following vessel ischemia may be stimulated through VEGFA gene therapy and/or MSC transplantation for reduction of ischemic injury in limb ischemia and heart failure. The therapeutic potential of MSC transplantation can be further improved by genetically modifying MSCs with genes which enhance angiogenesis following ischemic injury. In the present study, we aimed to develop an approach in MSC-based therapy for repair and mitigation of ischemic injury and regeneration of damaged tissues in ischemic disease. HSP70 promoter-driven VEGFA expression was induced by resveratrol (RSV) in MSCs, and in combination with known RSV biological functions, the protective effects of our approach were investigated by using ex vivo aortic ring coculture system and a 3D scaffolds in vivo model. Results of this investigation demonstrated that HSP promoter-driven VEGFA expression in MSC increased approximately 2-fold over the background VEGFA levels upon HSP70 promoter induction by RSV. Exposure of HUVEC cells to medium containing MSC in which VEGFA had been induced by cis-RSV enhanced tube formation in the treated HUVEC cells. RSV-treated MSC cells differentiated into endothelial-like phenotypes, exhibiting markedly elevated expression of endothelial cell markers. These MSCs also induced aortic ring sprouting, characteristic of neovascular formation from pre-existing vessels, and additionally promoted neovascularization at the MSC transplantation site in a mouse model. These observations support a hypothesis that VEGFA expression induced by cis-RSV acting on the HSP70 promoter in transplanted MSC augments the angiogenic effects of stem cell gene therapy. The use of an inducible system also vastly reduces possible clinical risks associated with constitutive VEGFA expression.     

Synaptopathy under conditions of altered gravity: Changes in synaptic vesicle fusion and glutamate release

Glutamate release and synaptic vesicle heterotypic/homotypic fusion were characterized in brain synaptosomes of rats exposed to hypergravity (10 G, 1 h). Stimulated vesicular exocytosis determined as KCl-evoked fluorescence spike of pH-sensitive dye acridine orange (AO) was decreased twice in synaptosomes under hypergravity conditions as compared to control. Sets of measurements demonstrated reduced ability of synaptic vesicles to accumulate AO (10% higher steady-state baseline level of AO fluorescence). Experiments with preloaded l-[¹⁴C]glutamate exhibited similar amount of total glutamate accumulated by synaptosomes, equal concentration of ambient glutamate, but the enlarged level of cytoplasmic glutamate measuring as leakage from digitonin-permeabilized synaptosomes in hypergravity. Thus, it may be suggested that +G-induced changes in stimulated vesicular exocytosis were a result of the redistribution of intracellular pool of glutamate, i.e. a decrease in glutamate content of synaptic vesicles and an enrichment of the cytoplasmic glutamate level. To investigate the effect of hypergravity on the last step of exocytosis, i.e. membrane fusion, a cell-free system consisted of synaptic vesicles, plasma membrane vesicles, cytosolic proteins isolated from rat brain synaptosomes was used. It was found that hypergravity reduced the fusion competence of synaptic vesicles and plasma membrane vesicles, whereas synaptosomal cytosolic proteins became more active to promote membrane fusion. The total rate of homo- and heterotypic fusion reaction initiated by Ca²⁺ or Mg²⁺/ATP remained unchanged under hypergravity conditions. Thus, hypergravity could induce synaptopathy that was associated with incomplete filling of synaptic vesicles with the neuromediator and changes in exocytotic release.     

Antitumor activity of L-asparaginase from Yersinia pseudotuberculosis

The cytotoxic activity of L-asparaginases from Yersinia pseudotuberculosis and from Erwinia carotovora were investigated in vitro using human T-lymphoblastic leukemia (Jurkat and Molt-4) and also solid tumor cell lines MCF-7 (human breast adenocarcinoma), LnCap (human prostate carcinoma), NGUK1 (rat Gasser node neurinoma). E.coli L-asparaginase produced by Medak (Germany) was used as a reference preparation. The data obtained indicate that Y. pseudotuberculosis L-asparaginase significantly inhibits growth of leukemic and solid tumor cells. Its antitumor activity is comparable to that of the reference preparation of L-asparaginase (Medak). These results suggest that the recombinant L-asparaginase can be used for the development of new preparations for the therapy of different types of tumors.     

Ester derivatives of annulated tetrahydroazocines: a new class of selective acetylcholinesterase inhibitors

A series of ester derivatives of annulated tetrahydroazocines, namely 2,3,6,11-tetrahydro-1H-azocino[4,5-b]indoles (5-10), 2,3,6,7-tetrahydro-1H-azocino[5,4-b]indoles (11-14), and 4,7,8,9-tetrahydro-1H-pyrrolo[2,3-d]azocines (15-18), synthesized through an efficient 6-->8 membered ring expansion procedure, were investigated for their acetylcholinesterase (AChE) inhibitory activities. Most of the compounds acted as AChE inhibitors in vitro, with IC(50) values ranging from 5 to 40 microM. The most potent compounds 11 and 15, both as racemic mixtures, proved selective toward AChE, exhibiting selectivity ratios versus butyrylcholinesterase (BuChE) of ca. 15 and more than 20, respectively. Structure-activity studies highlighted, among other factors, lipophilicity as a property modulating the AChE inhibition potency, as shown by a reasonable parabolic correlation between pIC(50) and experimental 1-octanol/water partition coefficient (logP), which described the prevailing behavior of the examined compounds (r(2)=0.665). Molecular docking simulations using the X-ray crystal structure of AChE from Torpedo californica suggested possible binding modes of the tetrahydroazocine ester derivatives 11 and 15.     

5,10,15,20-Tetra-(N-methyl-3-pyridyl)porphyrin destabilizes the anti-parallel telomeric quadruplex d(TTAGGG)4

We studied the parameters of binding of 5,10,15,20-tetra-(N-methyl-3-pyridyl)porphyrin (TMPyP3) to the anti-parallel human telomeric G-quadruplex d(TTAGGG)4, the oligonucleotide dTTAGGGTTAGAG(TTAGGG)2 that does not form a quadruplex structure, as well as to the double stranded d(AC)8 x d(GT) and single stranded d(AC)8 and d(GT)8 DNAs. The analysis of absorption revealed that the binding constants and the number of DNA binding sites for TMPyP3 were d(AC)8 < d(GT)8 < d(AC)8 x d(GT)8 = d(TTAGGG)4 < dTTAGGGTTAGAG(TTAGGG)2. We demonstrated for the first time that the binding constant of TMPyP3 with the non-quadruplex chain dTTAGGGTTAGAG(TTAGGG)2 (1.3 x 10(7) M(-1)) is approximately 3 times bigger than the binding constant with the quadruplex d(TTAGGG)4 (4.6 x 10(6) M(-1)). Binding of two TMPyP3 molecules to d(TTAGGG)4 led to a decrease of thermostability of the G-quadruplex (deltaT(m) = -8 degrees C). Circular dichroism spectra of TMPyP3:d(TTAGGG)4 complexes revealed a shift of DNA structure from the G-quadruplex to an irregular chain. We hypothesize that partial destabilization of the telomeric G-quadruplex by TMPyP3 might be a reason for relatively low potency of this ligand as a telomerase inhibitor, as well as its marginal cytotoxicity for cultured tumor cells.