SWI by 7T MR Imaging for the Microscopic Imaging Diagnosis of Astrocytic and Oligodendroglial Tumors

BACKGROUND AND PURPOSE

Despite advances in molecular imaging, preoperative diagnosis of astrocytomas and oligodendrogliomas can be challenging. In the present study, we assessed whether 7T SWI can be used to distinguish astrocytomas and oligodendrogliomas and whether malignant grading of gliomas is possible.

MATERIALS AND METHODS

7T SWI was performed on 21 patients with gliomas before surgery with optimization for sharp visualization of the corticomedullary junction. Scoring for cortical thickening and displacement of medullary vessels, characteristic of oligodendroglial tumors, and cortical tapering, characteristic of astrocytic tumors, was performed. Additionally, characteristics of malignancy, including thickening of the medullary veins, the presence of microbleeds, and/or necrosis were scored.

RESULTS

Scoring for oligodendroglial (highest possible score, +3) and astrocytic (lowest score possible, -3) characteristics yielded a significant difference between astrocytomas and oligodendrogliomas (mean, -1.93 versus +1.71, P < .01). Scoring for malignancy was significantly different among the World Health Organization grade II (n = 10), grade III (n = 4), and grade IV (n = 7) tumors (mean, 0.20 versus 1.38 versus 2.79). Cortical thickening was observed significantly more frequently in oligodendrogliomas (P < .02), with a sensitivity of 71.4% and specificity of 85.7%; observation of tapering of the cortex was higher in astrocytomas (P < .01) with a sensitivity of 85.7% and specificity of 100%.

CONCLUSIONS

Visualization of the corticomedullary junction by 7T SWI was useful in distinguishing astrocytomas and oligodendrogliomas. Observation of tapering of the cortex was most sensitive and specific for diagnosing astrocytomas. Reliably predicting malignant grade was also possible by 7T SWI.

Development of retake support system for lateral knee radiographs by using deep convolutional neural network

INTRODUCTION

Lateral radiography of the knee joint is frequently performed; however, the retake rate is high owing to positioning errors. Therefore, in this study, to reduce the required number and time of image retakes, we developed a system that can classify the tilting directions of lateral knee radiographs and evaluated the accuracy of the proposed method.

METHODS

Using our system, the tilting directions of a lateral knee radiographs were classified into four direction categories. The system was developed by training the DCNN based on 50 cases of Raysum images and tested on three types test dataset; ten more cases of Raysum images, one case of flexed knee joint phantom images and 14 rejected knee joint radiographs. To train a deep convolutional neural network (DCNN), we employed Raysum images created via three-dimensional (3D) X-ray computed tomography (CT); 11 520 Raysum images were created from 60 cases of 3D CT data by changing the projection angles. Thereby, we obtained pseudo images attached with correct labels that are essential for training.

RESULTS

The overall accuracy on each test dataset was 88.5 ± 7.0% (mean ± standard deviation), 81.4 ± 11.2%, and 73.3 ± 9.2%. The larger the tilting degree of the knee joint, the higher the classification accuracy.

CONCLUSION

DCNN could classify the tilting directions of a knee joint from lateral knee radiographs. Using Raysum images made it possible to facilitate creating dataset for training DCNN. The possibility was indicated for using support system of lateral knee radiographs.

IMPLICATIONS FOR PRACTICE

The system may also reduce the burden on patients and increase the work efficiency of radiological technologists.

Estimation of the following Cardiac Output Using Sympathetic Tone and Hemodynamics for the Control of a Total Artificial Heart

A sympathetic neurogram is potentially useful for the development of a real time total artificial heart (TAH) control system. We used sympathetic tone and hemodynamic derivatives to estimate the following cardiac output in acute animal experiments using adult mongrel dogs. Moving averages of the mean left atrial pressure and mean aortic pressure were used as parameters of the preload and afterload, respectively. Renal sympathetic nerve activity (RSNA) was employed as a parameter of sympathetic tone. Equations for the following cardiac output were calculated using multiple linear regression analysis of the time series data. A significant correlation was observed between the estimated and following measured cardiac output. These results suggest the potential usefulness of the sympathetic neurogram for the real time TAH automatic control system.

Collaboration of local government and experts responding to increase in environmental radiation level due to the nuclear disaster: focusing on their activities and latest radiological discussion

Activities were introduced in Kashiwa city in the Tokyo metropolitan area to correspond to the elevated environmental radiation level after the disaster of the Fukushima Daiichi nuclear power plant. These were based on a strong cooperation between local governments and experts. Ambient dose rate and radioactivity of foodstuff produced inside of the city have been monitored. Representative ambient dose rates around living environments have almost already become their original levels of the pre-accident because of the decontamination activity, natural washout and effective half-lives of radioactivity. The internal annual dose due to radioactive cesium under the policy of 'Local Production for Local Consumption' is estimated as extremely low comparing the variation range due to natural radioactivity. Systematic survey around a retention basin has been started. All of these latest monitoring data would be one of the core information for the policy making as well as a cost-benefit discussion and risk communication.

Purification and Characterization of a Thermostable Carboxypeptidase (CarboxypeptidaseTaq)fromThermus aquaticusYT-1

A thermostable carboxypeptidase, which we named carboxypeptidase Taq, was purified from Thermus aquaticus YT-1 and characterized. The molecular weight of the enzyme was estimated to be about 56,000 and 58,000 on SDS-polyacrylamide gel electrophoresis and gel filtration, respectively, indicating that the enzyme has a monomeric structure. The optimum pH of the enzyme was 8.0, and the optimum temperature for the reaction was 80 degrees C. The enzyme activity was dependent on cobalt ion and was inhibited by metal-chelating reagents, indicating that the enzyme is a metalloenzyme. The enzyme had high thermostability independent of cobalt ion; about 90% of its activity remained even after treatment at 80 degrees C for 5 h. The enzyme showed broad substrate specificity, although proline at the C-terminus of peptides was not cleaved. The enzyme released amino acids sequentially from the C-terminus.

Purification, crystallization and preliminary X-ray investigation of aqualysin I, a heat-stable serine protease

Aqualysin I, a thermostable protease found in the culture medium of Thermus aquaticus YT-1, has been purified to homogeneity using a combination of ion-exchange and affinity chromatography. It is a polypeptide with a molecular weight of 28 350 [Kwon, Terada, Matsuzawa & Ohta (1988). Eur. J. Biochem. 173, 491-497] and is most active at 343-353 K and pH about 10.0 [Matsuzawa, Tokugawa, Hamaoki, Mizoguchi, Taguchi, Terada, Kwon & Ohta (1988). Eur. J. Biochem. 171, 441-447]. Crystals of the enzyme are monoclinic, space group P2(1), with cell dimensions a = 40.80 (5), b = 64.39 (6), c = 45.51 (6) A and beta = 109.1 (1) degrees. The asymmetric unit consists of a single molecule (V(m) = 1.99 A(3)Da(-1)). The crystals are stable to X-radiation and scatter to at least 2.8 A resolution.

Acute lethal injury of lung and liver in mice transplanted with ex vivo-expanded CTLs

Clinical application of cytotoxic T lymphocytes (CTL) induced in vitro is extensively used for the treatment of viral infection and malignant diseases. We produced anti H-2d CTL in vitro from C57BL/6 (B6) splenocytes presensitized with (B6 x DBA/2) F1 (BDF1) splenocytes to establish a model system of CTL therapy. The specificity and cytotoxic activity were high enough (E/T ratio 1:1 = 38.8%) to induce graft versus host reaction. Though the total number of B6 splenocytes decreased by 0.27 during the 4 days of culture, the number of CD8+ lymphocytes increased 1.3-fold. When more than 5 x 10(6) cells of H-2d-reactive CTL were transplanted into BDF1 mice, mice died within 2 days postinduction. This lethal effect was not seen in the mice induced with ConA-stimulated T cells. Histological examination of the lungs and liver revealed massive infiltration of neutrophils in alveoli and the necrosis of hepatocytes. Therefore, this protocol was shown to be effective to produce alloantigen-specific CTLs and applicable to in vitro manipulation such as retrovirus-mediated gene transfer.

Role of a highly conserved YPITP motif in 2-oxoacid:ferredoxin oxidoreductase: heterologous expression of the gene from Sulfolobus sp.strain 7, and characterization of the recombinant and variant enzymes

2-Oxoacid:ferredoxin oxidoreductase from Sulfolobus sp. strain 7, an aerobic and thermoacidophilic crenoarchaeon, catalyses the coenzyme A-dependent oxidative decarboxylation of pyruvate and 2-oxoglutarate, a cognate Zn-7Fe-ferredoxin serving as an electron acceptor. It comprises two subunits, a (632 amino acids) and b (305 amino acids). To further elucidate its structure and function, we constructed a gene expression system. The wild-type recombinant enzyme was indistinguishable from the natural one in every criterion investigated. A series of variants was constructed to elucidate the role of the YPITP-motif (residues 253-257) in subunit a, which is conserved universally in the 2-oxoacid:ferredoxin oxidoreductase (OFOR) family. Single amino-acid replacements at Y253 and P257 by other amino acids caused a drastic loss of enzyme activity. T256, the hydroxyl group of which has been proposed to be essential for binding of the 2-oxo group of the substrate in the Desulfovibrio africanus enzyme, was unexpectedly replaceable with Ala, the kcat and Km for 2-oxoglutarate being approximately 33% and approximately 51%, respectively, as compared with that of the wild-type enzyme. Replacement at other positions resulted in a significant decrease in the kcat of the reaction while the Km for 2-oxoacid was only slightly affected. Thus, the YPITP-motif is essential for the turnover of the reaction rather than the affinity toward 2-oxoacid.

Identification of the catalytic residue of Thermococcus litoralis 4-alpha-glucanotransferase through mechanism-based labeling

Thermococcus litoralis 4-alpha-glucanotransferase (TLGT) belongs to family 57 of glycoside hydrolases and catalyzes the disproportionation and cycloamylose synthesis reactions. Family 57 glycoside hydrolases have not been well investigated, and even the catalytic mechanism involving the active site residues has not been studied. Using 3-ketobutylidene-beta-2-chloro-4-nitrophenyl maltopentaoside (3KBG5CNP) as a donor and glucose as an acceptor, we showed that the disproportionation reaction of TLGT involves a ping-pong bi-bi mechanism. On the basis of this reaction mechanism, the glycosyl-enzyme intermediate, in which a donor substrate was covalently bound to the catalytic nucleophile, was trapped by treating the enzyme with 3KBG5CNP in the absence of an acceptor and was detected by matrix-assisted laser desorption ionization time-of-flight mass spectrometry after peptic digestion. Postsource decay analysis suggested that either Glu-123 or Glu-129 was the catalytic nucleophile of TLGT. Glu-123 was completely conserved between family 57 enzymes, and the catalytic activity of the E123Q mutant enzyme was greatly decreased. On the other hand, Glu-129 was a variable residue, and the catalytic activity of the E129Q mutant enzyme was not decreased. These results indicate that Glu-123 is the catalytic nucleophile of TLGT. Sequence alignment of TLGT and family 38 enzymes (class II alpha-mannosidases) revealed that Glu-123 of TLGT corresponds to the nucleophilic aspartic acid residue of family 38 glycoside hydrolases, suggesting that family 57 and 38 glycoside hydrolases may have had a common ancestor.

Efficient lentiviral transduction of human cord blood CD34(+) cells followed by their expansion and differentiation into dendritic cells

OBJECTIVE

To support immune reconstitution after cord blood transplantation, immunotherapy using gene-modified dendritic cells (DCs), the most potent antigen-presenting cells, can be a powerful strategy for preventing infection and recurrence. To investigate the applicability of lentiviral vector-transduced DCs compared to retroviral vectors, we transduced umbilical cord blood (CB) CD34(+) cells, then expanded and differentiated them into DCs.

MATERIALS AND METHODS

We transduced CB CD34(+) cells by vesicular stomatitis virus G-protein pseudotyped self-inactivating lentiviral vector or retroviral vectors carrying the enhanced green fluorescent protein gene. The cells were expanded in the stroma-dependent culture system and transferred to the culture condition for developing DCs. The efficiency of transduction and expression of the transgene in severe combined immunodeficiency (SCID) mice-repopulating cells (SRCs) and DCs were compared between lentiviral vector and retroviral vectors. Induced DCs were cocultured with allogeneic or autologous T cells to test the ability to present antigens.

RESULTS

CB CD34(+) cells transduced by lentiviral vector and expanded ex vivo sustained stable transgene expression and multipotentiality by assessing SRCs assay and clonogenic assay of bone marrow cells from the transplanted mice. DCs derived from these cells expressed green fluorescent protein and surface markers CD1a, CD80, and HLA-DR and showed potent allo-stimulatory activity as well as nontransduced DCs did. On the other hand, we did not detect transgene expression in SRCs and DCs transduced by retroviral vectors.

CONCLUSION

Gene-modified DCs derived from ex vivo expanded CB CD34(+) cells transduced by lentiviral vector will be useful in future immunotherapy protocols.

HscA is involved in the dynamics of FtsZ-ring formation in Escherichia coli K12

BACKGROUND

FtsZ, a homologue of eukaryotic tubulin, localizes throughout the cytoplasm in non-dividing Escherichia coli. However, it assembles in cytokinetic rings at the early stages of septation. Factors controlling the dynamics of FtsZ ring formation are unknown, and the molecular mechanism governing these dynamics is yet to be determined.

RESULTS

At 42 degrees C, JE10715 mutant bacteria formed multinucleated filaments with a highly reduced number of FtsZ-rings at potential division sites. The JE10715 phenotype resulted from a mis-sense mutation in the hscA gene which encodes a heat shock Hsp70 family protein, with a single alanine-to-valine substitution at position 192 within the ATPase domain. Both JE10715 and the hscA knockout strain of JE10715 were completely complemented by a plasmid-born, wild-type hscA gene, but not by a mutant-type hscA715 gene. An hscA conditional knockout of the wild-type strain under non-permissive conditions exhibited longer rod cells with an abnormal localization of FtsZ. The over-expression of dnaK partially complemented the JE10715 mutation. In vitro, the ATPase activity of the mutant protein HscA715 was reduced to 63% of wild-type HscA activity. HscA co-sedimented with FtsZ-polymers in the presence of GTP.

CONCLUSION

HscA is involved in FtsZ-ring formation, through a chaperon-like interaction with FtsZ. Defects in hscA, however, can partially be compensated for by redundant genes, including the wild-type dnaK.

Three-dimensional anisotropy contrast magnetic resonance axonography to predict the prognosis for motor function in patients suffering from stroke

OBJECT

The purpose of this study was to assess how early wallerian degeneration in the corticospinal tracts of patients who had suffered from stroke was detected using three-dimensional anisotropy contrast (3D-AC) magnetic resonance (MR) axonography and to explore the possibility of predicting the prognosis for motor function in these patients.

METHODS

Ten healthy volunteers and 16 stroke patients with hemiparesis were studied using MR images including 3D-AC MR axonography images obtained using a 1.5-tesla MR imaging system. The axonography was performed using an echoplanar imaging method. All patients underwent MR studies 2, 3, and 10 weeks after stroke onset. To detect wallerian degeneration, the diffusion anisotropy in the corticospinal tracts at the level of the upper pons was evaluated on axial images. These MR findings were compared with the patients' motor functions, which were classified according to the Brunnstrom criteria 12 weeks after the onset of stroke. In all patients with poor recovery (Brunnstrom Stages I-IV), wallerian degeneration, which was demonstrated as a reduction in diffusion anisotropy on axonography images, could be observed in the corticospinal tracts; this degeneration was not found in patients with good recovery (Stages V and VI). Axonography could be used to detect degeneration between 2 and 3 weeks after stroke onset. On conventional T2-weighted MR images, hyperintense areas indicating wallerian degeneration were not detected until 10 weeks after stroke onset.

CONCLUSIONS

With the aid of 3D-AC MR axonography, wallerian degeneration can be detected in the corticospinal tracts during the early stage of stroke (2-3 weeks after onset), much earlier than it can be detected using T2-weighted MR imaging. The procedure of 3D-AC MR axonography may be useful in predicting motor function prognosis in stroke patients.

Structural basis for the ADP-specificity of a novel glucokinase from a hyperthermophilic archaeon

BACKGROUND

ATP is the most common phosphoryl group donor for kinases. However, certain hyperthermophilic archaea such as Thermococcus litoralis and Pyrococcus furiosus utilize unusual ADP-dependent glucokinases and phosphofructokinases in their glycolytic pathways. These ADP-dependent kinases are homologous to each other but show no sequence similarity to any of the hitherto known ATP-dependent enzymes.

RESULTS

We solved the crystal structure at 2.3 A resolution of an ADP-dependent glucokinase from T. litoralis (tlGK) complexed with ADP. The overall structure can be divided into large and small alpha/beta domains, and the ADP molecule is buried in a shallow pocket in the large domain. Unexpectedly, the structure was similar to those of two ATP-dependent kinases, ribokinase and adenosine kinase. Comparison based on three-dimensional structure revealed that several motifs important both in structure and function are conserved, and the recognition of the alpha- and beta-phosphate of the ADP in the tlGK was almost identical with the recognition of the beta- and gamma-phosphate of ATP in these ATP-dependent kinases.

CONCLUSIONS

Noticeable points of our study are the first structure of ADP-dependent kinase, the structural similarity to members of the ATP-dependent ribokinase family, its rare nucleotide specificity caused by a shift in nucleotide binding position by one phosphate unit, and identification of the residues that discriminate ADP- and ATP-dependence. The strict conservation of the binding site for the terminal and adjacent phosphate moieties suggests a common ancestral origin of both the ATP- and ADP-dependent kinases.

Enhancement of human cord blood CD34+ cell-derived NK cell cytotoxicity by dendritic cells

NK cells and dendritic cells (DCs) are both important in the innate host defense. However, the role of DCs in NK cell-mediated cytotoxicity is unclear. In this study, we designed two culture systems in which human cord blood CD34(+) cells from the same donor were induced to generate NK cells and DCs, respectively. Coculture of the NK cells with DCs resulted in significant enhancement of NK cell cytotoxicity and IFN-gamma production. However, NK cell cytotoxicity and IFN-gamma production were not increased when NK cells and DCs were grown together separated by a transwell membrane. Functional studies demonstrated that 1) concanamycin A, a selective inhibitor of perforin/granzyme B-based cytolysis, blocked DC-stimulated NK cytotoxicity against K562 cells; and 2) neutralizing mAb against Fas ligand (FasL) significantly reduced DC-stimulated NK cytotoxicity against Fas-positive Jurkat cells. In addition, a marked increase of FasL mRNA and FasL protein expression was observed in DC-stimulated NK cells. The addition of neutralizing mAb against IL-18 and IL-12 significantly suppressed DC-stimulated NK cell cytotoxicity. Neutralizing IFN-gamma Ab almost completely inhibited NK cell cytotoxicity against Jurkat cells. These observations suggest that DCs enhance NK cell cytotoxicity by up-regulating both perforin/granzyme B- and FasL/Fas-based pathways. Direct interaction between DCs and NK cells is necessary for DC-mediated enhancement of NK cell cytotoxicity. Furthermore, DC-derived IL-18 and IL-12 were involved in the up-regulation of NK cell cytotoxicity, and endogenous IFN-gamma production plays an important role in Fas-mediated cytotoxicity.

Folding pathway mediated by an intramolecular chaperone: the structural and functional characterization of the aqualysin I propeptide

Aqualysin I, a thermostable homologue of subtilisin, requires its propeptide (ProA) to function as an intramolecular chaperone (IMC). To decipher the mechanisms through which propeptides can initiate protein folding, we characterized ProA in terms of its sequence, structure and function. Our results show that, in contrast to ProS (propeptide of subtilisin), ProA can fold spontaneously, reversibly and cooperatively into a stable monomeric alpha-beta conformation, even when isolated from its cognate protease-domain. ProA displays an indiscernible amount of tertiary structure with a considerable solvent-accessible hydrophobic surface, but is not a classical molten-globule folding intermediate. Moreover, despite showing only 21 % sequence identity with ProS, ProA can not only inhibit enzymatic activity with a magnitude tenfold greater than ProS, but can also chaperone subtilisin folding, albeit with a lower efficiency. The structure of ProA complexed with subtilisin is different from that of isolated ProA. Hence, additional interactions seem necessary to induce ProA into a compact structure. Our results also suggest that: (a) propeptides that are potent inhibitors are not necessarily better IMCs; (b) propeptides within the subtilase family appear polymorphic and; (c) the intrinsic instability within propeptides may be necessary for rapid activation of the cognate protein.

Some Lactobacillus L-lactate dehydrogenases exhibit comparable catalytic activities for pyruvate and oxaloacetate

The nonallosteric and allosteric L-lactate dehydrogenases of Lactobacillus pentosus and L. casei, respectively, exhibited broad substrate specificities, giving virtually the same maximal reaction velocity and substrate K(m) values for pyruvate and oxaloacetate. Replacement of Pro101 with Asn reduced the activity of the L. pentosus enzyme toward these alternative substrates to a greater extent than the activity toward pyruvate.

Requirement for the COOH-terminal pro-sequence in the translocation of aqualysin I across the cytoplasmic membrane in Escherichia coli

Aqualysin I from Thermus aquaticus YT-1 is an extracellular subtilisin-type serine protease. The protease is synthesized as a distinct precursor composed of four functional domains: an N-terminal signal sequence, an N-terminal pro-sequence, a protease domain, and a C-terminal pro-sequence. The N-terminal pro-sequence is essential for the production of active aqualysin I while the C-terminal pro-sequence is required for extracellular secretion of aqualysin I. In an E. coli expression system, the function of C-terminal pro-sequence in the translocation of aqualysin I across the cytoplasmic membrane was investigated. More than 60-70% of the total activity was detected in the cytoplasmic fraction in the deletion mutations of the C-terminal pro-sequence while less than 30% was found in this fraction in wild type. In addition, in vitro processing of aqualysin I precursors with these mutations to a mature form promptly occurred and the folding into active aqualysin I was rapid. These results suggest that the C-terminal pro-sequence, probably in conjunction with the signal sequence, facilitates the translocation of the precursor across the cytoplasmic membrane by preventing the precursor from taking on an active conformation.

Application of a metal switch to aqualysin I, a subtilisin-type bacterial serine protease, to the S3 site residues, ser102 and gly131

We applied 'metal switch' experiments to the S3 site residues, Ser102 and Gly131, of aqualysin I, a subtilisin-type serine protease. We showed that two histidines introduced at these positions did take part in histidine-metal-histidine bridge formation, and metal ions inhibited the protease activities. These results indicate that two histidines are near each other, and both side chains are metal-accessible. This is the first report on application of the metal-switch technique to a subtilisin-related enzyme.

Independent component-cross correlation-sequential epoch (ICS) analysis of high field fMRI time series: direct visualization of dual representation of the primary motor cortex in human

A new technique for functional magnetic resonance imaging (fMRI) time series analysis is presented. The technique referred to here as independent component-cross correlation-sequential epoch (ICS) analysis is a hybrid technique of two standard methodologies of biological signal analysis, namely, data driven methods, represented by independent component analysis, and hypothesis driven methods, represented by a general linear model. The technique successfully identified four functionally discrete areas within the primary sensorimotor cortex (SMI) in normal human subjects based on blood oxygenation level dependent (BOLD) contrast functional magnetic resonance imaging (fMRI) time series performed on a high field (3.0 T) system. Each of the four areas identified corresponded to the four physiological subdivisions of SMI, recognized in primates to be essential for voluntary hand motion, namely, 4 anterior (MI-4a) and 4 posterior (MI-4p) of the primary motor cortex, and 3a and the 'classical' (Brodmann areas 1, 2, and 3b) primary sensory cortex, respectively. ICS analysis appears to be a highly reliable and versatile technique for fMRI time series analysis.

Extensive generation of human cord blood CD34(+) stem cells from Lin(-)CD34(-) cells in a long-term in vitro system

Human CD34(-) hematopoietic stem cells (HSCs) have been identified as potential precursors of CD34(+) HSCs by using xenogeneic transplantation systems. However, the properties of CD34(+) cells generated from CD34(-) cells have not been precisely analyzed due to the lack of an in vitro system in which CD34(+) cells are continuously produced from CD34(-) cells. We conducted this study to determine whether CD34(+) cells generated in vitro from CD34(-) cells have long-term multilineage reconstitution abilities. Lin(-)CD34(-) population isolated from human cord blood was cultured in the presence of murine bone marrow stroma cell line, HESS-5, and human cytokines, thrombopoietin, Flk2/Flt3 ligand, stem cell factor, granulocyte colony-stimulating factor, interleukin 3 (IL-3), and IL-6. They were analyzed weekly for their surface markers expressions, colony-forming cells, long-term culture initiating cells (LTC-IC), and SCID repopulating cells (SRC) abilities up to 30 days of culture. In this culture system, more than 10(7) CD34(+) cells can be continuously generated from 10(4) CD34(-) cells over 30 days. These CD34(+) cells produce colony-forming units, LTC-IC, and SRC with multi-lineage differentiation, all of which are characteristic features of hematopoietic stem/progenitor cells. These findings suggest that CD34(-) HSCs have extensive potential for the generation of CD34(+) HSCs in vitro. This system provides a novel and potentially useful procedure to generate CD34(+) cells for clinical transplantation and gene therapy.

Engineering subtilisin E for enhanced stability and activity in polar organic solvents

We examined the effect of a novel disulfide bond engineered in subtilisin E from Bacillus subtilis based on the structure of a thermophilic subtilisin-type serine protease aqualysin I. Four sites (Ser163/Ser194, Lys170/Ser194, Lys170/Glu195, and Pro172/Glu195) in subtilisin E were chosen as candidates for Cys substitutions by site-directed mutagenesis. The Cys170/Cys195 mutant subtilisin formed a disulfide bond in B. subtilis, and showed a 5-10-fold increase in specific activity for an authentic peptide substrate for subtilisin, N-succinyl-L-Ala-L-Ala-L-Pro-L-Phe-p-nitroanilide, compared with the single-Cys mutants. However, the disulfide mutant had a 50% decrease in catalytic efficiency due to a smaller k(cat) and was thermolabile relative to the wild-type enzyme, whereas it was greatly stabilized relative to its reduced form. These results suggest that an electrostatic interaction between Lys170 and Glu195 is important for catalysis and stability in subtilisin E. Interestingly, the disulfide mutant was found to be more stable in polar organic solvents, such as dimethylformamide and ethanol, than the wild-type enzyme, even under reducing conditions; this is probably due to the substitution of uncharged Cys by charged surface residues (Lys170 and Glu195). Further, the amino-terminal engineered disulfide bond (Gly61Cys/Ser98Cys) and the mutation Ile31Leu were introduced to enhance the stability and catalytic activity. A prominent 3-4-fold increase in the catalytic efficiency occurred in the quintet mutant enzyme over the range of dimethylformamide concentration (up to 40%).

Inhibitory effects of bovine lactoferrin on the adherence of enterotoxigenic Escherichia coli to host cells

Adherence is an essential and prerequisite step for the colonization of mucosal surfaces by enterotoxigenic Escherichia coli (ETEC). We studied the effect of bovine lactoferrin (BLF) on the adherence of ETEC to human epithelial cells in vitro, and to intestinal mucosa of ICR germfree mice in vivo. In the in vitro study, BLF was found to inhibit the adherence of ETEC. This adhesion-inhibiting activity of BLF was found to lessen with decreasing BLF concentration, but the data obtained suggest a positive inhibitory effect of BLF against the adhesion of ETEC cells. In the in vivo study, the counts of adherent bacteria in various sections of the intestinal tract (duodenum, jejunoileum, and large intestine) were lower in the BLF group than in the control group, suggesting the possible action of BLF as an intestinal tract adherence-blocking agent with regards to ETEC.

Second transmembrane segment of FtsH plays a role in its proteolytic activity and homo-oligomerization

The FtsH (HflB) protein of Escherichia coli is a membrane-bound ATP-dependent zinc protease. The role(s) of the N-terminal membrane-anchoring region of FtsH were studied by fusion with a maltose-binding protein (MBP) at five different N-termini of FtsH. The MBP-FtsH fusions were expressed in the cytoplasm of E. coli, and were purified as soluble proteins. The four longer constructs, which have a second transmembrane segment and the C-terminal cytoplasmic region in common, retained ATP-dependent protease activity toward heat-shock transcription factor sigma(32), and were found to be homo-oligomers. In contrast, the shortest construct which has the C-terminal cytoplasmic region but not the second transmembrane segment showed neither protease activity nor oligomerization. Therefore, the second transmembrane segment, which neighbors the C-terminal cytoplasmic region of the FtsH, participates in not only its membrane-anchoring, but also its protease activity and homo-oligomerization.

Perceptual processing of stereopsis in humans: high-field (3.0-tesla) functional MRI study

Cortical activation associated with stereopsis was studied in eight right-handed neurosurgeons professionally trained in stereoscopic vision. The activation map associated with viewing three-dimensional images, as contrasted to viewing the corresponding two-dimensional images of identical contents (images of MR angiography), showed consistent activation in the cortex adjacent to the intraparietal sulcus. The study further demonstrated a dominant role of the right hemisphere in perceptual processing of stereopsis in humans.

High level expression of Thermococcus litoralis 4-alpha-glucanotransferase in a soluble form in Escherichia coli with a novel expression system involving minor arginine tRNAs and GroELS

The Thermococcus litoralis 4-alpha-glucanotransferase (GTase) gene has a high content of AGA and AGG codons for arginine, which are extremely rare in Escherichia coli. Expression of the GTase gene in E. coli resulted in low protein production and the accumulation of inclusion bodies. However, simultaneous expression of GTase with tRNA(AGA), tRNA(AGG) and GroELS affected both the production and solubility of GTase, and production of soluble GTase increasing about 5-fold. This new E. coli expression system should be applicable to the expression of not only archaeal but also eukaryotic genes, which usually contain a large number of AGA and AGG codons.

Weakly bound calcium ions involved in the thermostability of aqualysin I, a heat-stable subtilisin-type protease of Thermus aquaticus YT-1

Aqualysin I is a heat-stable protease; in the presence of 1 mM Ca(2+), the enzyme is stable at 80 degrees C and shows the highest activity at the same temperature. After gel filtration to remove free Ca(2+) from the purified enzyme sample, the enzyme (holo-aqualysin I) still bound Ca(2+) (1 mol/mol of the enzyme), but was no longer stable at 80 degrees C. On treatment of the holo-enzyme with EDTA, bound Ca(2+) decreased to about 0.3 mol/mol of the enzyme. The thermostability of holo-aqualysin I was dependent on the concentration of added Ca(2+), and 1 mM added Ca(2+) stabilized the enzyme completely, suggesting that aqualysin I has at least two Ca(2+) binding sites, i.e. stronger and weaker binding ones. Titration calorimetry showed single binding of Ca(2+) to the holo-enzyme with an association constant of 3.1 x 10(3) M(-1), and DeltaH and TDeltaS were calculated to be 2.3 and 6.9 kcal/mol, respectively, at 13 degrees C. La(3+), Sr(2+), Nd(3+), and Tb(3+) stabilized the holo-enzyme at 80 degrees C, as Ca(2+) did. These results suggest that the weaker binding site exhibits structural flexibility to bind several metal cations different in size and valency, and that the metal binding to the weaker binding site is essential for the thermostability of aqualysin I.

Zinc and an N-terminal extra stretch of the ferredoxin from a thermoacidophilic archaeon stabilize the molecule at high temperature

Ferredoxin from the thermoacidophilic archaeon Sulfolobus sp. strain 7 has a 36-residue extra domain at its N-terminus and a 67-residue core domain carrying two iron-sulfur clusters. A zinc ion is held at the interface of the two domains through tetrahedral coordination of three histidine residues (-6, -19 and -34) and one aspartic acid residue (-76) [Fujii, T., Hata, Y., Oozeki, M., Moriyama, H., Wakagi, T., Tanaka, N. & Oshima, T. (1997) Biochemistry 36, 1505-1513]. To elucidate the roles of the novel zinc ion and the extra N-terminal domain, a series of truncated mutants was constructed: G1, V12, S17, G23, L31 and V38, which lack residues 0, 11, 16, 22, 30 and 37 starting from the N-terminus, respectively. A mutant with two histidine residues each replaced by an alanine residue, H16A/H19A, was also constructed. All the mutant ferredoxins had two iron-sulfur clusters, while zinc was retained only in G1 and V12. The thermal stability of the proteins was investigated by monitoring A408; the melting temperature (Tm) was approximately 109 degrees C for the natural ferredoxin, approximately 109 degrees C for G1, 97.6 degrees C for V12, 89.0 degrees C for S17, 89.2 degrees C for G23, 89.3 degrees C for L31, 82.1 degrees C for V38, and 89.4 degrees C for H16A/H19A. Km and Vmax values of 2-oxoglutarate:ferredoxin oxidoreductase for natural ferredoxin, G1, S17 and L31 were similar, suggesting that electron-accepting activities were not affected by the deletion. The combination of CD and fluorescent spectroscopic analyses with truncated mutant S17 indicated that not only the clusters but also the secondary and tertiary structures were simultaneously degraded at a Tm around 89 degrees C. These results unequivocally demonstrate that the zinc ion and certain parts, but not all, of the extra sequence stretch in the N-terminal domain are responsible not for function but for thermal stabilization of the molecule.

Identification and designing of the S3 site of aqualysin I, a thermophilic subtilisin-related serine protease

Aqualysin I is a bacterial subtilisin-related alkaline serine protease, originating in Thermus aquaticus YT-1. Based on computational analysis, we predicted that two residues, Ser102 and Gly131, form the S3 site of aqualysin I, and we proved that this prediction by site-directed mutagenesis. To alter the P3-specificity of the enzyme, we built a "wall" on the S3 site edge by introducing a bulky side chain at target sites. Six mutant proteins were prepared: S102H, S102K, S102E, G131H, G131K, and G131D. The mutant enzymes were examined with two kinetically typical peptides for aqualysin I, suc-X-Ala-Ala-pNA, where X is Ala or Phe. All mutations reduced the efficiency for the Phe-containing peptide, while they raised the k(cat) values for the Ala-containing peptide. Especially, the S102K mutant protein hydrolyzed the polyalanine peptide efficiently. The strategies we have adopted in this paper are applicable to all subtilisin-related enzymes.

Magnetic resonance angiography for detection of occlusive neck and proximal vascular diseases

We reviewed magnetic resonance (MR) aortographies of the thoraco-cervical region of 422 patients. Two hundred sixty patients had ischemic cerebrovascular disease, 86 vertigo or dizziness, 22 syncope, 4 ischemic disease of the retina, 3 cervical bruit, and 47 had other intracranial diseases. MR aortography was performed on a 1.5 Tesla MRI using a special head-and-neck coil. Images were obtained using an overlapping multi-slab and three-dimensional time-of-flight technique. Of the 422 patients, 59 underwent conventional angiography, and the findings from their conventional arteriogram were compared with those of MR aortography. As a result, steno-occlusive lesions were found in the carotid system in 21.1% of the patients, in the vertebral system in 18.5%, and in the subclavian and innominate arteries in 2.1%. The diagnoses made based on the MR aortography were in accord with the diagnoses made with conventional arteriography in 49 patients (83.1%). In 8 patients (13.6%), however, the diagnosis based on the MR aortography was found to be overestimated compared with the definitive diagnosis with conventional angiography. In only 2 patients (3.3%), the MR aortography diagnosis was insufficient. Especially, subclavian steal was not diagnosed with the MR aortography, whereas the findings from the MR aortography helped to lead to the diagnosis of this abnormality. In conclusion, we found that MR aortography is a useful tool as a screening test for patients with occlusive extracranial cerebrovascular disease.

Properties of a subtilisin-like proteinase from a psychrotrophic Vibrio species comparison with proteinase K and aqualysin I

An extracellular serine proteinase purified from cultures of a psychrotrophic Vibrio species (strain PA-44) belongs to the proteinase K family of the superfamily of subtilisin-like proteinases. The enzyme is secreted as a 47-kDa protein, but under mild heat treatment (30 min at 40 degrees C) undergoes autoproteolytic cleavage on the carboxyl-side of the molecule to give a proteinase with a molecular mass of about 36 kDa that apparently shares most of the enzymatic characteristics and the stability of the 47-kDa protein. In this study, selected enzymatic properties of the Vibrio proteinase were compared with those of the related proteinases, proteinase K and aqualysin I, as representative mesophilic and thermophilic enzymes, respectively. The catalytic efficiency (kcat/Km) for the amidase activity of the cold-adapted enzyme against succinyl-AAPF-p-nitroanilide was significantly higher than that of its mesophilic and thermophilic counterparts, especially when compared with aqualysin I. The stability of the Vibrio proteinase, both towards heat and denaturants, was found to be significantly lower than of either proteinase K or aqualysin I. One or more disulfide bonds in the psychrotrophic proteinase are important for the integrity of the active enzyme structure, as disulfide cleavage, either by reduction with dithiothreitol or by sulfitolysis, led to a loss in its activity. Under the same conditions, aqualysin I was also partially inactivated by dithiothreitol, but the activity of proteinase K was unaffected. The disulfides of either proteinase K or aqualysin I were not reactive towards sulfitolysis, except under denaturing conditions, while all disulfides of the Vibrio proteinase reacted in absence of a denaturant. The reactivity of the disulfides of the proteins as a function of denaturant concentration followed the order: Vibrio proteinase > proteinase K > aqualysin I. The same order of reactivity was also observed for the inactivation of the enzymes by H2O2-oxidation, as a function of temperature. The order of reactivity observed in these reactions most likely reflects the accessibility of the reactive cystine or methionine side chains present in the three related proteinases, and hence a difference in the compactness of their protein structures.

Crystal structure of the E166A mutant of extended-spectrum beta-lactamase Toho-1 at 1.8 A resolution

Bacterial resistance to beta-lactams is mainly due to the production of beta-lactamase. Especially through the production of extended-spectrum beta-lactamases (ESBLs), bacteria have acquired resistance not only to penicillins, but also to expanded-spectrum cephems. Here, we describe the crystal structure of the E166A mutant of class A beta-lactamase Toho-1 at 1.8 A resolution, the first reported tertiary structure of an ESBL. Instead of the wild-type enzyme, a mutant Toho-1, in which Glu166 was replaced with alanine, was used for this study, because of the strong tendency of the wild-type enzyme to form twinned crystals. The overall structure of Toho-1 is similar to the crystal structures of non-ESBLs, with no pronounced backbone rearrangement of the framework. However, there are some notable local changes. First, a difference in the disposition of an arginine residue, which is at position 244 in non-ESBLs but at position 276 in Toho-1 and other ESBLs, was revealed and the role of this arginine residue is discussed. Moreover, changes in the hydrogen-bonding pattern and in the formation of the hydrophobic core were also observed near the Omega loop. In particular, the lack of hydrogen bonds in the vicinity of the Omega loop could be a cause of the extended substrate specificity of Toho-1. Through the generation of a model for the enzyme-substrate complex, a conformational change of Toho-1 occurring on complex formation is discussed based on the active-site cleft structure and the substrate profile.

Balanced biosynthesis of major membrane components through regulated degradation of the committed enzyme of lipid A biosynthesis by the AAA protease FtsH (HflB) in Escherichia coli

The suppressor mutation, named sfhC21, that allows Escherichia coli ftsH null mutant cells to survive was found to be an allele of fabZ encoding R-3-hydroxyacyl-ACP dehydrase, involved in a key step of fatty acid biosynthesis, and appears to upregulate the dehydrase. The ftsH1(Ts) mutation increased the amount of lipopolysaccharide at 42 degrees C. This was accompanied by a dramatic increase in the amount of UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase [the IpxC (envA) gene product] involved in the committed step of lipid A biosynthesis. Pulse-chase experiments and in vitro assays with purified components showed that FtsH, the AAA-type membrane-bound metalloprotease, degrades the deacetylase. Genetic evidence also indicated that the FtsH protease activity for the deacetylase might be affected when acyl-ACP pools were altered. The biosynthesis of phospholipids and the lipid A moiety of lipopolysaccharide, both of which derive their fatty acyl chains from the same R-3-hydroxyacyl-ACP pool, is regulated by FtsH.

Engineering of S2 site of aqualysin I; alteration of P2 specificity by excluding P2 side chain

Gly101, one of the conserved amino acid residues which was expected to be comprised in half-sphere-shaped S2 site small pocket of aqualysin I, a microbial thermophilic alkaline serine protease, was replaced by alanine, valine, or leucine to alterate the P2 specificity of the enzyme by excluding bulky P2 side chain of the substrate. By the mutation of G101A, the catalytic efficiencies of the enzyme for bulky amino acid residues in P2 site such as valine and leucine drastically decreased by excluding the P2 side chain. By the mutation of G101V, even the side chain of the methyl group of the alanine and the side chain of proline were excluded, while the catalytic efficiency toward glycine residue was retained. The enzyme was altered to be glycine preferable. The mutation of G101L reduced catalytic efficiencies for any substrate including glycine which is corresponding to the main chain of the peptide substrate. The strategies we have adopted in this paper are applicable to all subtilisin-related enzymes.

Cloning of the gene for inorganic pyrophosphatase from a thermoacidophilic archaeon, Sulfolobus sp. strain 7, and overproduction of the enzyme by coexpression of tRNA for arginine rare codon

The gene encoding an extremely stable inorganic pyrophosphatase from Sulfolobus sp. strain 7, a thermoacidophilic archaeon, was cloned and sequenced. An open reading frame consisted of 516 base pairs coding for a protein of 172-amino acid residues. The deduced sequence was supported by partial amino acid sequence analyses. All the catalytically important residues were conserved. A unique 17-base-pair sequence motif was found to be repeated four times in frame in the gene, encoding a cluster of acidic amino acids essential for the function. Although the codon usage of the gene was quite different from that of Escherichia coli, the gene was effectively expressed in E. coli. Coexpression of tRNA(Arg), cognate for the rare codon AGA in E. coli, however, further improved the production of the enzyme, which occupied more than 85% of the soluble proteins obtained after removal of heat denatured E. coli proteins.

Crystallographic and mutational analyses of an extremely acidophilic and acid-stable xylanase: biased distribution of acidic residues and importance of Asp37 for catalysis at low pH

Xylanase C from Aspergillus kawachii has an optimum pH of 2.0 and is stable at pH 1.0. The crystal structure of xylanase C was determined at 2.0 A resolution (R-factor = 19.4%). The overall structure was similar to those of other family 11 xylanases. Asp37 and an acid-base catalyst, Glu170, are located at a hydrogen-bonding distance (2.8 A), as in other xylanases with low pH optima. Asp37 of xylanase C was replaced with asparagine and other residues by site-directed mutagenesis. Analyses of the wild-type and mutant enzymes showed that Asp37 is important for high enzyme activity at low pH. In the case of the asparagine mutant, the optimum pH shifted to 5.0 and the maximum specific activity decreased to about 15% of that of the wild-type enzyme. On structural comparison with xylanases with higher pH optima, another striking feature of the xylanase C structure was found; the enzyme has numerous acidic residues concentrated on the surface (so-called 'Ser/Thr surface' in most family 11 xylanases). The relationship of the stability against extreme pH conditions and high salt concentrations with the spatially biased distribution of charged residues on the proteins is discussed.

Purification and characterization of a feruloylesterase from Aspergillus awamori

A feruloylesterase was purified from the extracellular broth of Aspergillus awamori grown on wheat bran culture. The purified enzyme gave a single band on SDS-polyacrylamide gel electrophoresis and isoelectric focusing, with an apparent M(r) of 35,000 and a pI of 3.8, respectively. The substrate specificity of the purified enzyme differed obviously from that of acetylesterase of A. awamori. The enzyme bound to microcrystalline cellulose.

P1 specificity of aqualysin I (a subtilisin-type serine protease) from Thermus aquaticus YT-1, using P1-substituted derivatives of Streptomyces subtilisin inhibitor

Aqualysin I is an alkaline serine protease isolated from Thermus aquaticus YT-1, an extreme thermophile. We have measured the P1-specificity of aqualysin I, using wild-type and five P1-substituted derivatives of Streptomyces subtilisin inhibitor (SSI). SSIs efficiently inhibited the activity of aqualysin I, with low substrate specificity. Charge and hydrophobicity of side chain of the P1 amino acid residue showed no significant effect to the P1-specificity of this enzyme.

Thermostable beta-galactosidase from an extreme thermophile, Thermus sp. A4: enzyme purification and characterization, and gene cloning and sequencing

We purified and characterized a thermophilic beta-galactosidase from Thermus sp. A4 isolated from the Atagawa hot spring (Shizuoka, Japan). The enzyme was monomeric, and its molecular mass was estimated to be 75 kDa by SDS-polyacrylamide gel electrophoresis. The enzyme was extremely thermostable and retained its full activity after incubation at 70 degrees C for 20 h. The Km observed were 5.9 mM for ortho-nitrophenyl beta-D-galactopyranoside and 19 mM for lactose. We cloned and analyzed the complete sequence of the gene encoding this enzyme. It was found to consist of 645 amino acid residues. We propose that this enzyme and seven other unclassified beta-galactosidases are new members of family 42 of the glycosyl hydrolases.

ftsE(Ts) affects translocation of K+-pump proteins into the cytoplasmic membrane of Escherichia coli

The ftsE(Ts) mutation of Escherichia coli causes defects in cell division and cell growth. We expressed alkaline phosphatase (PhoA) fusion proteins of KdpA, Kup, and TrkH, all of which proved functional in vivo as K+ ion pumps, in the mutant cells. During growth at 41 degrees C, these proteins were progressively lost from the membrane fraction. The reduction in the abundance of these proteins inversely correlated with cell growth, but the preformed proteins in the membrane were stable at 41 degrees C, indicating that the molecules synthesized at the permissive temperature were diluted in a growth-dependent manner at a high temperature. Pulse-chase experiments showed that KdpA-PhoA was synthesized, but the synthesized protein did not translocate into the membrane of the ftsE(Ts) cells at 41 degrees C and degraded very rapidly. The loss of KdpA-PhoA from the membrane fractions of ftsE(Ts) cells was suppressed by a multicopy plasmid carrying the ftsE+ gene. While cell growth stopped when the abundance of these proteins decreased 15-fold, the addition of a high concentration of K+ ions specifically alleviated the growth defect of ftsE(Ts) cells but not cell division, and the cells elongated more than 100-fold. We conclude that one of the causes of growth cessation in the ftsE(Ts) mutants is a defect in the translocation of K+-pump proteins into the cytoplasmic membrane.

Cloning and sequencing of the gene encoding Toho-2, a class A beta-lactamase preferentially inhibited by tazobactam

Escherichia coli TUM1083, which is resistant to ampicillin, carbenicillin, cephaloridine, cephalothin, piperacillin, cefuzonam, and aztreonam while being sensitive to cefoxitin, moxalactam, cefmetazole, ceftazidime, and imipenem, was isolated from the urine of a patient treated with beta-lactam antibiotics. The beta-lactamase (Toho-2) purified from the bacteria hydrolyzed beta-lactam antibiotics such as penicillin G, carbenicillin, cephaloridine, cefoxitin, cefotaxime, ceftazidime, and aztreonam and especially had increased relative hydrolysis rates for cephalothin, cephaloridine, cefotaxime, and ceftizoxime. Different from other extended-spectrum beta-lactamases, Toho-2 was inhibited 16-fold better by the beta-lactamase inhibitor tazobactam than by clavulanic acid. Resistance to beta-lactams was transferred by conjugation from E. coli TUM1083 to E. coli ML4909, and the transferred plasmid was about 54.4 kbp, belonging to the incompatibility group IncFII. The cefotaxime resistance gene for Toho-2 was subcloned from the 54.4-kbp plasmid. The sequence of the gene was determined, and the open reading frame of the gene was found to consist of 981 bases. The nucleotide sequence of the gene (DDBJ accession no. D89862) designated as bla(toho) was found to have 76.3% identity to class A beta-lactamase CTX-M-2 and 76.2% identity to Toho-1. It has 55.9% identity to SHV-1 beta-lactamase and 47.5% identity to TEM-1 beta-lactamase. Therefore, the newly isolated beta-lactamase designated as Toho-2 produced by E. coli TUM1083 is categorized as an enzyme similar to Toho-1 group beta-lactamases rather than to mutants of TEM or SHV enzymes. According to the amino acid sequence deduced from the DNA sequence, the precursor consisted of 327 amino acid residues. Comparison of Toho-2 with other beta-lactamase (non-Toho-1 group) suggests that the substitutions of threonine for Arg-244 and arginine for Asn-276 are important for the extension of the substrate specificity.

Conversion of neopullulanase-alpha-amylase from Thermoactinomyces vulgaris R-47 into an amylopullulanse-type enzyme

TVA I, an alpha-amylase from Thermoactinomyces vulgaris R-47, is a versatile enzyme which hydrolyzes the alpha-(1-->4)-glucosidic linkages of pullulan to produce panose, known as neopullulanase activity, and the alpha-(1-->6)-glucosidic linkages of certain oligosaccharides. We modified the Ala-357, Gln-359, and Tyr-360 residues located in region II, one of the four regions conserved in alpha-amylase family enzymes, and deleted 11 consecutive amino acid residues located after the C-terminus of region II of the TVA I sequence by means of site-directed mutagenesis. The action pattern of the mutated enzyme for pullulan was greatly altered and it hydrolyzed mainly the alpha-(1-->6)-glucosidic linkages of pullulan to produce maltotriose, while the action patterns for starch and maltooligosaccharides were almost identical to those of the wild-type enzyme. This means that the mutated TVA I has lost the neopullulanase activity, and thus can be designated as an amylopullulanase-type enzyme. The kcat/Km value of the mutated enzyme for alpha-(1-->6)-glucosidic linkages was virtually unaltered, while that for alpha-(1-->4)-glucosidic linkages was about 100 times smaller than that of the wild-type enzyme.

Homotropic activation via the subunit interaction and allosteric symmetry revealed on analysis of hybrid enzymes of L-lactate dehydrogenase

L-Lactate dehydrogenase from Bifidobacterium longum shows homotropic activation by pyruvate as well as heterotropic activation by fructose 1,6-bisphosphate. Hybrid enzymes were produced from the wild-type subunit and a mutant subunit, whose substrate specificity was altered to that of malate dehydrogenase, and separated to analyze the substrate-induced homotropic activation mechanism. Oxamate, a competitive inhibitor of L-lactate dehydrogenase, was used to mimic the substrate-induced activation of the wild-type subunit as "a regulatory subunit." The malate dehydrogenase activity of the mutant subunit as "the catalytic subunit" of the hybrid enzymes was measured, and the activity of the mutant subunit was activated on the addition of oxamate. Thus, we directly observed the inter-subunit homotropic activation transmitted from the wild-type to the mutant subunit. Moreover, "isomeric" hybrid enzymes that have different structural subunit arrangements but identical subunit compositions showed identical kinetic natures. This indicates that the enzyme maintains its subunit symmetry during the allosteric transition.

Role of the COOH-terminal pro-sequence of aqualysin I (a heat-stable serine protease) in its extracellular secretion by Thermus thermophilus

Aqualysin I is a subtilisin-type serine protease secreted into the medium by Thermus aquaticus YT-1. Thermus thermophilus cells harboring a plasmid for the aqualysin I precursor secreted pro-aqualysin I with the C-terminal pro-sequence into the culture medium, and the precursor was then processed to the mature enzyme during the cultivation. However, the extracellular levels of aqualysin I in T. thermophilus cells harboring plasmids for deletion mutants as to the C-terminal pro-sequence were about 10-20% in comparison with the level of wild-type. Only the mature enzyme could be detected in the medium, while pro-aqualysin I with the C-terminal pro-sequence could not. These results suggest that the C-terminal pro-sequence of aqualysin I plays an important role in the extracellular secretion of aqualysin I.

Inhibitory effect on LPS-induced tumor necrosis factor in calves treated with chlorpromazine or pentoxifylline

The inhibitory effect of chlorpromazine (CPZ), pentoxifylline (PTX) and dexamethasone (DEX) was investigated in a model of endotoxin shock in Holstein calves following an intravenous administration of Esherichia coli endotoxin (LPS). Initial correlations with its effects on the levels of tumor necrosis factor (TNF), a pivotal mediator of endotoxin shock, and clinical signs were obtained. The pretreatment of CPZ or DEX significantly decreased the serum levels of TNF, and reduced endotoxic shock. But the pretreatment of PTX hardly reduced the increase of serum TNF levels and endotoxin shock. The levels of serum endotoxin were not significantly different a minute of postinjection of LPS in calves. The results of this study indicate that pretreatment of CPZ or DEX inhibit various biological effects on endotoxin in calves.

Involvement of Glu-264 and Arg-235 in the essential interaction between the catalytic imidazole and substrate for the D-lactate dehydrogenase catalysis

For Lactobacillus pentosus D-lactate dehydrogenase, the binding of 2-ketoacids is markedly stabilized through interactions between the protonated imidazole of His-296, an acid/base catalyst of the enzyme, and the carbonyl oxygen of 2-ketoacids. The replacement of Arg-235 with Gln destabilized the inhibitory binding of oxamate much more than that of formate, acetate, or propionate, and the Arg to Lys substitution specifically diminished only oxamate binding. On the other hand, replacement of a conserved Glu, Glu-264, with Gln severely impaired the enzyme activity and markedly reduced affinity to 2-keto acids. The pH dependence of the oxamate inhibition revealed that the substitutions of Arg-235 and Glu-264 induced a great loss of the imidazole-carbonyl interaction. However, replacement of Glu-264 with Asp, another acidic amino acid, affected the enzyme function less than the Glu to Gln substitution. In addition, both the Arg-235 and Glu-264 substitutions induced marked increases in the primary isotope effect on the catalysis, suggesting that these amino acids stimulate the hydrogen transfer step in the catalysis. We concluded, therefore, that the guanidino and carboxyl groups of Arg-235 and Glu-264, respectively, cooperatively promote the essential imidazole-substrate interaction, enhancing the substrate binding and catalysis.

An Aspergillus awamori acetylesterase: purification of the enzyme, and cloning and sequencing of the gene

An inducible acetylesterase was purified from the culture medium of Aspergillus awamori strain IFO4033 growing on wheat-bran culture by ion-exchange, gel-filtration and hydrophobic-interaction chromatographies. The purified enzyme had an Mr of 31000 and contained Asn-linked oligosaccharides. The enzyme liberated acetic acid from wheat bran, hydrolysed only alpha-naphthyl acetate and propionate when aromatic esters were used for the substrate, and was tentatively classified as a carboxylic esterase (EC 3.1.1.1). The gene encoding acetylesterase was cloned and sequenced. The deduced amino acid sequence showed that acetylesterase was produced as a 304-amino-acid-residue precursor, which was converted post-translationally into a 275-amino-acid-residue mature protein. Part of the sequence of acetylesterase was similar to the region near the active-site serine of lipases of Geotrichum candidum and Candida cylindracea. A unique site of putative Asn-linked oligosaccharides was presented.

4-alpha-glucanotransferase from the hyperthermophilic archaeon Thermococcus litoralis--enzyme purification and characterization, and gene cloning, sequencing and expression in Escherichia coli

4-Alpha-Glucanotransferase was purified from cells of Thermococcus litoralis, a hyperthermophilic archaeon. The molecular mass of the enzyme was estimated to be approximately 87 kDa by gel filtration. The optimal temperature for its activity was 90 degrees C. The enzyme catalyzed the transglycosylation of maltooligosaccharides, yielding maltooligosaccharides of various lengths and glucose. When maltoheptaose was used as the substrate, glucoamylase-resistant and glucoamylase-sensitive saccharides were produced. On incubation of amylose with the T. litoralis enzyme, glucoamylase-resistant but alpha-amylase-sensitive molecules were produced, but the amount of reducing sugar showed only slight increases. These results indicate that the T. litoralis enzyme catalyzes not only intermolecular transglycosylation to produce linear alpha-1,4-glucan, but also intramolecular transglycosylation to produce cyclic alpha-1,4-glucan (cycloamylose), similarly to potato 4-alpha-glucanotransferase (called disproportionating enzyme). The gene encoding the T. litoralis 4-alpha-glucanotransferase was cloned, sequenced and expressed in Escherichia coli. The nucleotide sequence of the gene encoded a 659-amino acid protein with a calculated molecular mass of 77,883 Da. The amino acid sequence of the T. litoralis enzyme showed high similarity with those of alpha-amylases of Pyrococcus furiosus, a hyperthermophilic archaeon, and Dictyoglomus thermophilum, an extremely thermophilic bacterium, but little similarity with those of other known 4-alpha-glucanotransferases.

[Magnetic resonance axonography by diffusion weighted echo planar imaging]

Anisotropy of apparent diffusivities of water molecules is known to be an excellent means for elucidating detailed information regarding neuronal fiber direction and density in live subjects. The recent development of magnetic resonance axonography (MRX) utilizing three dimensional anisotropy contrast(3DAC), using Echo Planar Imaging(EPI), a new algorithm for the treatment of apparent diffusion tensor, has provided an unprecedented opportunity for visualizing anatomic detail of the human brain. In this study, we applied the 3DAC method in normal human brain. The results clearly demonstrated that 3DAC is highly sensitive to orientation of fiber tracts. Considering the rather simple implementational process and high anatomic resolution, MRX based on the 3DAC method appears to be the ideal non-invasive imaging technique for assessment of the human brain in biomedicine.