Roles for MreC and MreD proteins in helical growth of the cylindrical cell wall in Bacillus subtilis

Actin homologues of the MreB family have an important role in specifying the morphology of many non-spherical eubacteria. The mreC and mreD genes have been implicated in control of cell morphology but their precise functions are unknown. In Bacillus subtilis the MreB homologue Mbl directs helical insertion of new cell wall material in the cylindrical part of the rod-shaped cell. Depletion of either MreC or MreD abolishes the control of cell shape. In the presence of high concentrations of magnesium cells depleted of MreC or MreD can be propagated indefinitely, although they have a spheroidal shape. We show that growth of the spheroidal mutants is based on insertion of new wall material at cell division sites and that this localized growth is dependent on cell division. Under some conditions the MreC and MreD proteins localize in a helical configuration. This localization pattern resembles that of the helical cables of Mbl protein. These results suggest that MreC and MreD act in a morphogenic pathway that couples the helical cytosolic Mbl cables to the extracellular cell wall synthetic machinery, which is critical for cylindrical elongation of the rod-shaped cells.

Enzymological characterization of FII(a), a fibrinolytic enzyme from Agkistrodon acutus venom

AIM

To study the enzymological characterization of a fibrinolytic enzyme (FII(a)) from Agkistrodon acutus venom.

METHODS

The fibrinogenolytic effect and the influences of several protease inhibitors, chelating agents, and metal ions on fibrinogenolytic activity were visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The metal content of FII(a) was determined by atomic absorption spectroscopy.

RESULTS

After incubation with FII(a) (0.25 g/L), Aalpha-, Bbeta- and gamma-chains of fibrinogen disappeared within 5 min, 30 min, and 8 h , respectively. The molecular weights of major degradation products were 45,000 and 41,000, which were different from those bands produced by plasmin. The fibrinogenolytic activity of FIIa was strongly inhibited by ethylenediamine tetraacetic acid (EDTA), ethyleneglycol tetraacetic acid (EGTA), dithiothreitol and cysteine, but not by phenylmethyl-sulfonyl fluoride and soybean trypsin inhibitor. Zinc (3171+/-25 mg/kg), potassium (489+/-17 mg/kg) and calcium (319+/-13 mg/kg) were found in FIIa. Zn2+, Ca2+ and Mg2+ could recover the fibrinogenolytic activity of FIIa, which was inhibited by EDTA. Only Ca2+ could recover the fibrinogenolytic activity inhibited by EGTA.

CONCLUSION

FIIa can degrade the Aalpha-, Bbeta- and gamma-chains of fibrinogen. FII(a) is a metalloproteinase, and Zn2+, Ca2+, and disulfide bonds are necessary for its fibrinogenolytic activity.

Trypanosoma rangeli: characterization of a Mg-dependent ecto ATP-diphosphohydrolase activity

In this work we describe the ability of living Trypanosoma rangeli to hydrolyze extracellular ATP. In these intact parasites whose viability was assessed before and after the reactions by motility and by Trypan blue dye exclusion, there was a low level of ATP hydrolysis in the absence of any divalent metal (1.53+/-0.12 nmol P(i)/h x 10(7) cells). The ATP hydrolysis was stimulated by MgCl(2) and the Mg-dependent ecto-ATPase activity was 5.24+/-0.64 nmol P(i)/h x 10(7) cells. The Mg-dependent ecto-ATPase activity was linear with cell density and with time for at least 60 min. This stimulatory effect on the ATP hydrolysis was also observed when MgCl(2) was replaced by MnCl(2), but not by CaCl(2), SrCl(2), and ZnCl(2). The apparent K(m) for Mg-ATP2- was 0.53+/-0.11 mM. The optimum pH for the T. rangeli Mg-dependent ecto-ATPase activity lies in the alkaline range. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A1, ouabain, furosemide, vanadate, molybdate, sodium fluoride, tartrate, and levamizole. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, DIDS (4, 4'-diisothiocyanostylbene 2'-2'-disulfonic acid) as well as suramin, an antagonist of P2 purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. This ecto-ATPase activity was stimulated by carbohydrates involved in the attachment/invasion of salivary glands of Rhodnius prolixus and by lipophorin, an insect lipoprotein circulating in the hemolymph.

Effects of HMGN1 on chromatin structure and SWI/SNF-mediated chromatin remodeling

The dynamic modulation of chromatin structure is determined by many factors, including enzymes that modify the core histone proteins, enzymes that remodel the structure of chromatin, and factors that bind to genomic DNA to affect its structure. Previous work indicates that the nucleosome binding family of high mobility group proteins (HMGN) facilitates the formation of a chromatin structure that is more conducive for transcription. SWI/SNF complexes are ATP-dependent chromatin remodeling enzymes that alter nucleosome structure to facilitate the binding of various regulatory proteins to chromatin. Here we examine the structural consequences of reconstituting chromatin with HMGN1 and the resulting effects on hSWI/SNF function. We demonstrate that HMGN1 decreases the sedimentation velocity of nucleosomal arrays in low ionic strength buffers but has little effect on the structure of more highly folded arrays. We further demonstrate that HMGN1 does not affect SWI/SNF-dependent chromatin remodeling on either mononucleosomes or nucleosomal arrays, indicating that SWI/SNF functions independently of HMGN1.

Calcium ion promotes yeast Dmc1 activity via formation of long and fine helical filaments with single-stranded DNA

Dmc1 is specifically required for homologous recombination during meiosis. Here we report that the calcium ion enabled Dmc1 from budding yeast to form regular helical filaments on single-stranded DNA (ssDNA) and activate its strand assimilation activity. Relative to magnesium, calcium increased the affinity of Dmc1 for ATP and but reduces its DNA-dependent ATPase activity. These effects, together with previous studies of other RecA-like recombinases, support the view that ATP binding to Dmc1 protomers is required for functional filament structure. The helical pitch of the Saccharomyces cerevisiae Dmc1-ssDNA helical filament was estimated to be 13.4 +/- 2.5 nm. Analysis of apparently "complete" Dmc1-ssDNA filaments indicated a stoichiometry of 24 +/- 2 nucleotides per turn of the Dmc1 helix. This finding suggests that the number or protomers per helical turn and/or the number of nucleotides bound per Dmc1 protomer differs from that reported previously for Rad51 and RecA filaments. Our data support the view that the active form of Dmc1 protein is a helical filament rather than a ring. We speculate that Ca(2+) plays a significant role in regulating meiotic recombination.

Cytidine deaminase activity inPenicillium politans NRC-510

Cell-free extracts of nitrate-grown Penicillium politans NRC-510 catalyzes the hydrolytic deamination of cytidine to uridine. Uridine was chromatographically identified in cell-free extracts. The enzyme exhibited optimum pH and temperature activities at 6.5 and 80 degrees C respectively. Thermal stability experiments indicated that the enzyme restored its activity at 80 degrees C for at least 60 minutes. When cell-free extracts were incubated at 90 degrees C for 5 minutes enzyme activity was inhibited by about 33%. The involvement of sulfhydryl group(s) in the catalytic site of the enzyme was shown. HgCl2 (5 x 10(-3) M) and CuSO4 (10(-2) M) caused a complete inhibition of enzyme activity. Ethylene diamine tetraacetate at a concentration of 5 x 10(-3) M and 10(-2) M inhibited the enzyme as well. Whereas, MgCl2, CoSO2 and MnCl2 had a remarkable activating effect. Dialysis of the cell-free extracts resulted to an increase in enzyme activity by about 30%. To our knowledge the thermophilic nature of the cytidine deaminase of P. politans NRC-510 is unique.

5-HT1A receptor-mediated G protein activation assessed by [35S]GTPgammaS binding in rat cerebral cortex

To date, 5-hydroxytryptamine1A (5-HT1A) receptor-mediated functional assays (adenylyl cyclase inhibition, high-affinity GTPase activity and [35S]guanosine-5'-O-(gamma-thio)-triphosphate ([35S]GTPgammaS) binding) have been performed mainly in hippocampal membranes. In the current study, 5-HT-stimulated G protein activation assays were carried out in rat cerebral cortical membranes. High-affinity GTPase activity was stimulated by 5-HT, but not by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). By contrast, 5-HT- and 8-OH-DPAT-stimulated [35S]GTPgammaS binding displayed sufficient dynamic range enough to warrant further pharmacological analysis. Under standard conditions, which were determined precisely in terms of the concentrations of GDP, MgCl2 and NaCl, the profile of 5-HT-stimulated [35S]GTPgammaS binding investigated using a series of 5-HT receptor agonists and antagonists clearly indicated the involvement of the 5-HT1A receptor subtype. There appeared to be no evidence supporting the presence of regional heterogeneity in coupling efficiency between 5-HT1A and G proteins in the hippocampus or cortex. This method is a useful tool for investigating functional coupling between postsynaptic 5-HT1A receptors and G proteins in cerebral cortical membranes.

Characterization of an ecto-ATPase activity in Cryptococcus neoformans

Cryptococcus neoformans is the causative agent of pulmonary cryptococcosis and cryptococcal meningoencephalitis, which are major clinical manifestations in immunosuppressed patients. In the present study, a surface ATPase (ecto-ATPase) was identified in C. neoformans yeast cells. Intact yeasts hydrolyzed adenosine-5'-triphosphate (ATP) at a rate of 29.36+/-3.36nmol Pi/hx10(8) cells. In the presence of 5 mM MgCl(2), this activity was enhanced around 70 times, and an apparent K(m) for Mg-ATP corresponding to 0.61mM was determined. Inhibitors of phosphatases, mitochondrial Mg(2+)-ATPases, V-ATPases, Na(+)-ATPases or P-ATPases had no effect on the cryptococcal ATPase, but extracellular impermeant compounds reduced enzyme activity in living cells. ATP was the best substrate for the cryptococcal ecto-enzyme, but it also efficiently hydrolyzed inosine 5'-triphosphate (ITP), cytidine 5'-triphosphate (CTP), guanosine 5'-triphosphate (GTP) and uridine-5'-triphosphate (UTP). In the presence of ATP, C. neoformans became less susceptible to the antifungal action of fluconazole. Our results are indicative of the occurrence of a C. neoformans ecto-ATPase that may have a role in fungal physiology.

Anions or cations: who is in charge of inhibiting the nickel(II) promoted B- to Z-DNA transition?

Various weakly binding cations and anions were studied at a concentration of 10 mM to ascertain their interaction with the nickel(II) promoted B- to Z-DNA transition of poly d(GC). These salts were ranked according to the decreasing amounts of nickel needed for the B- to Z-DNA transition and provided the following order: NaCl approximately Me4NCl > LiCl >> MgCl2 > no salt > NaBF4 approximately NaNO3 approximately NaClO4. Remarkably, it was found that going from sodium nitrate to sodium chloride increased the necessary amount of nickel to induce the transition to the left-handed helix of poly d(GC) by a factor of 10. This dramatic effect cannot be explained by the binding constant of nickel(II) to chloride to form the monocationic complex. We believe that this is the first reported example of the role of chloride anions, which appear to modulate the interaction of nickel(II) ions with the polyanionic DNA.

Pre-Injury Magnesium Treatment Prevents Traumatic Brain Injury–Induced Hippocampal ERK Activation, Neuronal Loss, and Cognitive Dysfunction in the Radial-Arm Maze Test

We studied the effect of pre-injury magnesium (Mg(2+)) treatment on hippocampal extracellular signal- regulated kinase (ERK) activation induced by lateral fluid-percussion (FP) brain injury, and on working and reference memory in the radial-arm maze test in rats subjected to such traumatic brain injury (TBI) (n = 56) or to sham injury (n = 12). In the ipsilateral hippocampus, an increase in the phospho-ERK level was detected at 10 min after injury in rats subjected to FP brain injury of moderate severity (1.9-2.0 atm) as compared to sham-injured controls (p < 0.01), and was maintained for at least 120 min after injury (p < 0.05). In the contralateral hippocampus, the phospho-ERK level was transiently increased at 10 min after injury but fell to nearly its basal level by 30 min. When MgCl(2) solution (150 micromol) was infused intravenously from 20 min to 5 min before injury (n = 4-5), brain injury-induced ERK activation was significantly inhibited in the ipsilateral hippocampus at 60 min but not at 10 min after injury. Mg(2+) treatment also significantly prevented injury- induced neuronal loss in the ipsilateral hippocampus (p < 0.05 vs. vehicle-treated, brain-injured controls). At 2 weeks after injury, Mg2+ treatment was found to have significantly prevented injury-induced impairments in working (p < 0.0001 vs. vehicle-treated, brain-injured controls) and reference memory (p < 0.05) in the radial-arm maze test. The present study demonstrates that pretreatment with Mg(2+) prevents post-traumatic hippocampal ERK activation and neuronal loss, and cognitive dysfunction in the radial-arm maze test.

Direct Observation of Anomalous Single-Molecule Enzyme Kinetics

We report the direct measurement of the single-molecule enzymatic cleavage rates of ApaI-DNA complex in the presence of various concentrations of MgCl2 solution with total internal reflection fluorescence microscopy. We made use of the native adsorption properties of the two 12-base sticky ends of the DNA molecules to partially immobilize and stretch out the ApaI-DNA complex onto a glass surface. Synchronous initiation of reaction was achieved by the influx of Mg2+ solution. Once the DNA was cut, the two fragments (38 and 10 kb) would either collapse or further stretch out depending on the solution flow. The time required for cleaving each ApaI-lambda-DNA complex was recorded and analyzed. At low concentrations, the higher the concentration of Mg2+, the faster the DNA was cut. However, Mg2+ ion is no longer the limiting factor when its concentration is greater than 5 mM. A surprising result is that at all concentrations the decrease in intact DNA population as a function of time is linear rather than exponential. This suggests that there exists a distribution of ApaI conformations around the restriction site.

UMP kinase from Streptococcus pneumoniae: evidence for co-operative ATP binding and allosteric regulation

UMP kinase catalyses the phosphorylation of UMP by ATP to yield UDP and ADP. In prokaryotes, the reaction is carried out by a hexameric enzyme, activated by GTP and inhibited by UTP. In the present study, Streptococcus pneumoniae UMP kinase was studied as a target for antibacterial research and its interest was confirmed by the demonstration of the essentiality of the gene for cell growth. In the presence of MnCl2 or MgCl2, the saturation kinetics of recombinant purified UMP kinase was hyperbolic for UMP (K(m)=0.1 mM) and sigmoidal for ATP (the substrate concentration at half-saturation S0.5=9.4+/-0.7 mM and n=1.9+/-0.1 in the presence of MgCl2). GTP increased the affinity for ATP and decreased the Hill coefficient (n). UTP decreased the affinity for ATP and only slightly increased the Hill coefficient. The kcat (175+/-13 s(-1) in the presence of MgCl2) was not affected by the addition of GTP or UTP, whose binding site was shown to be different from the active site. The hydrodynamic radius of the protein similarly decreased in the presence of ATP or GTP. There was a shift in the pH dependence of the activity when the ATP concentration was switched from low to high. These results support the hypothesis of an allosteric transition from a conformation with low affinity for ATP to a form with high affinity, which would be induced by the presence of ATP or GTP.

Formation of volutin granules in Corynebacterium glutamicum

Volutin granules are intracellular storages of complexed inorganic polyphosphate (poly P). Histochemical staining procedures differentiate between pathogenic corynebacteria such as Corynebacterum diphtheriae (containing volutin) and non-pathogenic species, such as C. glutamicum. Here we report that strains ATCC13032 and MH20-22B of the non-pathogenic C. glutamicum also formed subcellular entities (18-37% of the total cell volume) that had the typical characteristics of volutin granules: (i) volutin staining, (ii) green UV fluorescence when stained with 4',6-diamidino-2-phenylindole, (iii) electron-dense and rich in phosphorus when determined with transmission electron microscopy and X-ray microanalysis, and (iv) 31P NMR poly P resonances of isolated granules dissolved in EDTA. MgCl2 addition to the growth medium stimulated granule formation but did not effect expression of genes involved in poly P metabolism. Granular volutin fractions from lysed cells contained polyphosphate glucokinase as detected by SDS-PAGE/MALDI-TOF, indicating that this poly P metabolizing enzyme is present also in intact poly P granules. The results suggest that formation of volutin is a more widespread phenomenon than generally accepted.

Natrinema altunense sp. nov., an extremely halophilic archaeon isolated from a salt lake in Altun Mountain in Xinjiang, China

A novel extremely halophilic strain, AJ2T, was isolated from Ayakekum salt lake located in the Altun Mountain National Nature Reserve in Xinjiang, China. This isolate was neutrophilic, motile and grew in a wide range of MgCl2 concentrations (0·005–1·0 M). The major polar lipids of the isolate were C20C20 and C20C25 derivatives of phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and phosphatidylglycerol sulfate. A comprehensive 16S rRNA gene sequence analysis revealed that the isolate shared 96·6–97·7 % sequence identity with Natrinema species. The isolate, however, could be genetically differentiated from these species by DNA–DNA hybridization analysis and on the basis of its physiological properties. On the basis of the polyphasic evidence, strain AJ2T (=AS 1.3731T=JCM 12890T) represents the type strain of a novel species, for which the name Natrinema altunense sp. nov. is proposed.

Matrix Protein–Specific Regulation of Cx43 Expression in Cardiac Myocytes Subjected to Mechanical Load

To elucidate mechanisms responsible for mechanotransduction in the heart and define the effects of remodeling of the extracellular matrix, we cultured neonatal rat ventricular myocytes on native type I collagen, fibronectin, or denatured collagen and subjected them to uniaxial, pulsatile stretch. Changes in expression of the cardiac gap junction protein, Cx43, were measured by confocal microscopy and immunoblotting. Cells grown on fibronectin or denatured collagen exhibited significantly greater Cx43 expression than cells grown on native collagen. Stretch induced a approximately 2-fold increase in Cx43 expression in cells grown on native collagen but no increase in cells grown on fibronectin or denatured collagen. Incubation of cells on native collagen with a peptide containing the arginine-glycine-aspartate (RGD) motif upregulated Cx43 expression equivalent to that induced by stretch. Nonselective activation of integrin signaling with MnCl2 also upregulated Cx43 expression in cells grown on native collagen. This effect was blocked completely by pretreatment with anti-beta1 integrin antibody but not by anti-beta3 integrin antibody. Stretch led to a marked increase in beta1 integrin immunofluorescent signal in cells grown on native collagen but not in cells grown on fibronectin or denatured collagen. Stretch-induced upregulation of Cx43 was also blocked by anti-beta1 integrin antibody. Thus, matrix protein-myocyte interactions regulate Cx43 expression via beta1 integrin signaling initiated by mechanical stimulation in cells grown on native type I collagen, or by RGD-integrin signaling independent of mechanical stress in cells grown on fibronectin or denatured collagen. Changes in the composition of the extracellular matrix may affect electrical coupling in cardiac myocytes.

Characterization of a thermophilic DNA ligase from the archaeon Thermococcus fumicolans

A PCR protocol was used to identify and sequence a gene encoding a DNA ligase from Thermococcus fumicolans (Tfu). The recombinant enzyme, expressed in Escherichia coli BL21(DE3) pLysS, was purified to homogeneity and characterized. The optimum temperature and pH of Tfu DNA ligase were 65 degrees C and 7.0, respectively. The optimum concentration of MgCl2, which is indispensable for the enzyme activity, was 2 mM. We showed that Tfu DNA ligase displayed nick joining and blunt-end ligation activity using either ATP or NAD+, as a cofactor. In addition, our results would suggest that Tfu DNA ligase is likely to use the same catalytic residues with the two cofactors. The ability for DNA ligases, to use either ATP or NAD+, as a cofactor, appears to be specific of DNA ligases from Thermococcales, an order of hyperthermophilic microorganisms that belongs to the euryarchaeotal branch of the archaea domain.

Kinetic studies on Na+/K+-ATPase and inhibition of Na+/K+-ATPase by ATP

Na+/K+-ATPase (EC 3.6.1.3) is an important membrane-bound enzyme. In this paper, kinetic studies on Na+/K+-ATPase were carried out under mimetic physiological conditions. By using microcalorimeter, a thermokinetic method was employed for the first time. Compared with other methods, it provided accurate measurements of not only thermodynamic data (deltarHm) but also the kinetic data (Km and Vmax). At 310.15K and pH 7.4, the molar reaction enthalpy (deltarHm) was measured as -40.514 +/- 0.9kJmol(-1). The Michaelis constant (Km) was determined to be 0.479 +/- 0.020 mM and consistent with literature data. The reliability of the thermokinetic method was further confirmed by colorimetric studies. Furthermore, a simple and reliable kinetic procedure was presented for ascertaining the true substrate for Na+/K+-ATPase and determining the effect of free ATP. Results showed that the MgATP complex was the real substrate with a Km value of about 0.5mM and free ATP was a competitive inhibitor with a Ki value of 0.253 mM.

The role of the regulatory subunit of fission yeast calcineurin for in vivo activity and its relevance to FK506 sensitivity

Calcineurin, a protein phosphatase required for Ca2+ signaling in many cell types, is a heterodimer composed of catalytic and regulatory subunits. The fission yeast genome encodes a single set of catalytic (Ppb1) and regulatory (Cnb1) subunits, providing an ideal model system to study the functions of these subunits in vivo. Here, we cloned the cnb1+ gene and showed that the cnb1 knock-out (Deltacnb1) exhibits identical phenotypes with Deltappb1 and that overexpression of Ppb1 failed to suppress the phenotypes of Deltacnb1. Interestingly, overexpression of the C-terminal-deleted Ppb1 (Ppb1DeltaC), the constitutively active form of Ppb1, also failed to suppress the phenotypes of Deltacnb1. FK506 caused MgCl2 sensitivity to the wild-type cells in an FKBP12-dependent manner. Co-overexpression of Ppb1 and Cnb1 suppressed the FK506-induced MgCl2 sensitivity, but the suppression was only partial, suggesting that an excess amount of the Ppb1-Cnb1 complex cannot compete out the FKBP12-FK506 complex. Although overexpression of Ppb1DeltaC alone had little effect on cell growth, co-overexpression of Ppb1DeltaC and Cnb1 caused a distinct growth defect. FK506 suppressed the growth defect when Cnb1 was co-expressed using the attenuated nmt1 promoter, but it failed to suppress the defect when Cnb1 was co-expressed using the wild-type nmt1 promoter. Knock-out of the prz1+ gene, encoding a downstream target transcription factor of calcineurin, suppressed the growth defect irrespective of the promoter potency. These results suggest that Cnb1 is essential for the activation of calcineurin and that the activated calcineurin is the pharmacological target of the FKBP12-FK506 complex in vivo.

Differential role of inhibition in habituation of two independent afferent pathways to a common motor output

Many studies of the neural mechanisms of learning have focused on habituation, a simple form of learning in which a response decrements with repeated stimulation. In the siphon-elicited siphon withdrawal reflex (S-SWR) of the marine mollusk Aplysia, the prevailing view is that homosynaptic depression of primary sensory afferents underlies short-term habituation. Here we examined whether this mechanism is also utilized in habituation of the tail-elicited siphon withdrawal reflex (T-SWR), which is triggered by an independent, polysynaptic afferent pathway that converges onto the same siphon motor neurons (MNs). By using semi-intact preparations in which tail and/or siphon input to siphon MNs could be measured, we found that repeated tail stimuli administered in the presence of a reversible conduction block of the nerves downstream of the tail sensory neurons (SNs) completely abolished the induction of habituation. Subsequent retraining revealed no evidence of savings, indicating that the tail SNs and their immediate interneuronal targets are not the locus of plasticity underlying T-SWR habituation. The networks closely associated with the siphon MNs are modulated by cholinergic inhibition. We next examined the effects of network disinhibition on S-SWR and T-SWR habituation using an Ach receptor antagonist d-tubocurarine. We found that the resulting network disinhibition disrupted T-SWR, but not S-SWR, habituation. Indeed, repeated tail stimulation in the presence of d-tubocurarine resulted in an initial enhancement in responding. Lastly, we tested whether habituation of T-SWR generalized to S-SWR and found that it did not. Collectively, these data indicate that (1) unlike S-SWR, habituation of T-SWR does not involve homosynaptic depression of SNs; and (2) the sensitivity of T-SWR habituation to network disinhibition is consistent with an interneuronal plasticity mechanism that is unique to the T-SWR circuit, since it does not alter S-SWR.

Transcapsidation and the conserved interactions of two major structural proteins of a pair of phytoreoviruses confirm the mechanism of assembly of the outer capsid layer

The strongly conserved amino acid sequences of the P8 outer capsid proteins of Rice dwarf virus (RDV) and Rice gall dwarf virus (RGDV) and the distribution of electrostatic potential on the proteins at the interfaces between structural proteins suggested the possibility that P8-trimers of RGDV might bind to the 3-fold symmetrical axes of RDV core particles, with vertical interaction between heterologous P3 and P8 proteins and lateral binding of homologous P8 proteins, thereby allowing formation of the double-layered capsids that are characteristic of viruses that belong to the family Reoviridae. We proved this hypothesis using chimeric virus-like particles composed of the P3 core capsid protein of RDV and the P8 outer capsid protein of RGDV, which were co-expressed in a baculovirus expression system. This is the first report on the molecular biological proof of the mechanism of the assembly of the double-layered capsids with disparate icosahedral lattices.

Treatment with magnesium improves reference memory but not working memory while reducing GFAP expression following traumatic brain injury

PURPOSE

Previous studies have shown that administration of MgCl2 in animal models of brain injury significantly improves functional recovery: however, few studies have examined cognitive recovery. The present study evaluated the effect of MgCl2 pharmacotherapy on recovery of function following medial frontal cortex contusion injury.

METHODS

Groups of rats were assigned to either MgCl2 (1.0 mmol/kg) or saline treatment conditions and prepared with contusion injuries or shams. Drug treatment was administered 15 min and 24 hr following injury. Rats were examined on tests of sensorimotor performance (bilateral tactile adhesive removal) and cognitive ability (reference and working memory).

RESULTS

Administration of MgCl2 following injury significantly reduced the behavioral impairments observed on the bilateral tactile removal test. The acquisition of reference memory was also significantly improved compared to saline-treated rats; however, treatment did not improve working memory performance. Lesion analysis revealed that administration of MgCl2 did not significantly reduce lesion size compared to saline-treatment. Examination of glial fibrillary acidic protein (GFAP) expression showed that MgCl2 did significantly reduce the number of GFAP+ cells.

CONCLUSION

These results indicate that MgCl2 administration significantly improved behavioral outcome following injury in a task dependent manner and reduced GFAP expression.

[Adenosine triphosphate-dependence of volume sensitive chloride current in LNCaP cell line of human prostate cancer]

Although sensitivity to intracellular ATP is considered to be one of the hallmarks of swelling activated Cl- current (I(Cl,swell)) involved in regulatory volume decrease (RVD) following hypotonic stress, the type and manner of such sensitivity seems to vary in different cell types. Here by using whole-cell patch-clamp recording we investigated ATP sensitivity of I(Cl,swell) in LNCaP human prostate cancer cell line. Suppression of endogenous ATP production with metabolic inhibitors (oligomycin, iodoacetate and rotenone) during cell dialysis with ATP- and Mg2+-free pipette solution did not prevent I(Cl,swell) in response to hypotonic exposure. However, supplementing this solution with 5 mM Na-ATP led to the development of I(Cl,swell) with nearly 305 higher density and less pronounced voltage-dependent inactivation (manifested mainly by the increase of non-inactivated current component) at positive potentials. On the contrary, inclusion of 1 mM Mg2+ in the patch pipette resulted in even smaller I(Cl,swell) (30% lower density compared to Mg2+-free conditions), which inactivated completely on prolonged depolarization. The presence of 5 mM Mg-ATP in the pipette did not affect I(Cl,swell) density. Neither intervention significantly altered the rate of I(Cl,swell) development in response to hypotonicity. We conclude that intracellular ATP, a positive modulator of I(Cl,swell)-carrying volume-regulated anion channel (VRAC) in LNCaP cells most likely acts via binding rather than hydrolysis and/or phosphorylation reactions, whereas intracellular Mg2+ is VRAC inhibitor.

Rea1, a dynein-related nuclear AAA-ATPase, is involved in late rRNA processing and nuclear export of 60 S subunits

Rea1, the largest predicted protein in the yeast genome, is a member of the AAA(+) family of ATPases and is associated with pre-60 S ribosomes. Here we report that Rea1 is required for maturation and nuclear export of the pre-60 S subunit. Rea1 exhibits a predominantly nucleoplasmic localization and is present in a late pre-60 S particle together with members of the Rix1 complex. To study the role of Rea1 in ribosome biogenesis, we generated a repressible GAL::REA1 strain and temperature-sensitive rea1 alleles. In vivo depletion of Rea1 results in the significant reduction of mature 60 S subunits concomitant with defects in pre-rRNA processing and late pre-60 S ribosome stability following ITS2 cleavage and prior to the generation of mature 5.8 S rRNA. Strains depleted of the components of the Rix1 complex (Rix1, Ipi1, and Ipi3) showed similar defects. Using an in vivo 60 S subunit export assay, a strong accumulation of the large subunit reporter Rpl25-GFP (green fluorescent protein) in the nucleus and at the nuclear periphery was seen in rea1 mutants at restrictive conditions.

[Influence of Mg ions and spermine on ATP-dependent Ca2+ transport in myometrial intracellular structures. II. Comparative study of spermine, Mg ions and cyclosporin A effects on Ca2+ transport in mitochondria]

In experiments carried out with the use of the radioactive label (45Ca2+) on suspension of the rat uterus myocytes processed by digitonin solution (0.1 mg/ml), influence of spermine and cyclosporin A on Mg2+, ATP-dependent Ca2+ transport in mitochondria at different Mg2+ concentration were investigated. Ca2+ accumulation in mitochondria was tested as such which was not sensitive to thapsigargin (100 nM) and was blocked by ruthenium red (10 microM). It has been shown, that spermine (1 mM) stimulates Mg2+, ATP-dependent Ca2+ accumulation in mitochondria irrespective of Mg2+ concentration (3 or 7 mM) in the incubation medium. At the same time cyclosporin A (5 microM) effects on Ca2+ accumulation in mitochondria depend on Mg2+ concentration in the incubation medium: at 3 mM Mg2+ the stimulating effect was observed, and at 7 mM Mg2+ - the inhibitory one. In conditions which led to the increase of nonspecific mitochondrial permeability and, accordingly, to dissipation of electrochemical potential (it was reached by 5 min. preincubation of myocytes suspension in the medium that contained 10 microM Ca2+, 2 mM phosphate and 3 or 7 mM Mg2+, but not ATP) significant inhibition of Mg2+, ATP-dependent Ca2+ accumulation in mitochondria was observed. The inhibition to the greater degree was observed when medium ATP and Mg2+ were absent simultaneously in the preincubation. Thus the quality of spermine effects on Ca2+ accumulation was kept: stimulation in the presence both of 3 mM and 7 mM Mg2+. Ca2+ accumulation did not reach the control level when 3 mM Mg2+ and 1 mM spermine was present and ATP absent in the preincubation medium. However, in the presence of 7 mM Mg2+ and 1 mM spermine practically full restoration (up to a control level) of Ca2+ accumulation was observed. At the same time with other things being equal such restoration was not observed at simultaneous absence of ATP and Mg2+ in the preincubation medium. The quality of cyclosporin A effects on Ca2+ accumulation in mitochondria was also kept: stimulation - in the presence of 3 mM Mg2+, inhibition - in the presence of 7 mM Mg2+ in the preincubation medium. And, at last, in the presence of cyclosporin A irrespective of the fact which preincubation medium was used, Ca2+ accumulation level practically did not depend on Mg2+ concentration.