Arrangement and symmetry of the fungal E3BP-containing core of the pyruvate dehydrogenase complex.

The pyruvate dehydrogenase complex (PDC) is a multienzyme complex central to aerobic respiration, connecting glycolysis to mitochondrial oxidation of pyruvate. Similar to the E3-binding protein (E3BP) of mammalian PDC, PX selectively recruits E3 to the fungal PDC, but its divergent sequence suggests a distinct structural mechanism. Here, we report reconstructions of PDC from the filamentous fungus Neurospora crassa by cryo-electron microscopy, where we find protein X (PX) interior to the PDC core as opposed to substituting E2 core subunits as in mammals. Steric occlusion limits PX binding, resulting in predominantly tetrahedral symmetry, explaining previous observations in Saccharomyces cerevisiae. The PX-binding site is conserved in (and specific to) fungi, and complements possible C-terminal binding motifs in PX that are absent in mammalian E3BP. Consideration of multiple symmetries thus reveals a differential structural basis for E3BP-like function in fungal PDC.

Effects of High-Voltage Electric Field Treatment on Bread Starch.

Bread dough was subjected to a high-voltage electric field (HVEF) during the first fermentation, and the bread firmness and the crystallinity of the starch (intensity of diffraction peak at 17.08° 2θ assigned to 4a; 5.24 Å d-spacing) isolated from the breads, which had been stored at 4 and 20°C, were examined. The HVEF treatment had the effects of reducing the bread firming at both storage temperatures as compared to the untreated bread. In this study, unexpected results were obtained for the crystallinity in the HVEF treated bread starches: while the firmness of the treated bread increased considerably after the first 3 days of storage at both temperatures, the rate of development in crystallinity was retarded at 20°C as compared with that of the untreated bread, but the opposite effect was observed at 4°C; that is, storing the bread at 4°C, the treated bread starch increased in crystallinity. These findings strongly suggest that crumb firming of the bread is involved in its water retention ability, taking into account the fact that the HVEF treatment made it possible to maintain bread softness longer than was possible for untreated bread. We, therefore, concluded that the increase in bread firmness was not closely related to the crystallinity of the bread starch, but was more influenced by the storage temperature.

Protein crystallization in microgravity.

A space experiment involving protein crystallization was conducted in a microgravity environment using the space shuttle "Endeavour" of STS-47, on a 9-day mission from September 12th to 20th in 1992. The crystallization was carried out according to a batch method, and 5 proteins were selected as flight samples for crystallization. Two of these proteins: hen egg-white lysozyme and co-amino acid: pyruvate aminotransferase from Pseudomonas sp. F-126, were obtained as single crystals of good diffraction quality. Since 1992 we have carried out several space experiments for protein crystallization aboard space shuttles and the space station MIR. Our experimental results obtained mainly from hen egg-white lysozyme are described below, focusing on the effects of microgravity on protein crystal growth.

Effects of DS-4574, a new orally active antiallergic agent, in experimental allergic and inflammatory models.

The anti-allergic and anti-inflammatory activities of DS-4574, which possesses leukotriene antagonism and inhibits the release of immunologically stimulated mediators such as histamine and leukotrienes, were evaluated in several animal models. DS-4574 had dose-dependent inhibitory effects on IgE-mediated passive cutaneous anaphylaxis and the passive Arthus reaction in rats and the phase I response of Forssman antibody-induced bronchoconstriction. In contrast, this compound had no effect on the phase II response of Forssman antibody-induced bronchoconstriction in guinea pigs, the reverse cutaneous anaphylaxis in rats, complement-dependent hemolysis of sheep erythrocytes and the delayed-type hypersensitivity induced by methylated bovine serum albumin in mice. The results obtained in a double sensitization with two IgE antibodies suggested that DS-4574, as well as disodium cromoglycate, did not impair antigen-antibody combination but prevents the release of chemical mediators such as histamine. DS-4574 also had a weak inhibitory activity on carrageenin paw edema in rats, arachidonic acid ear edema in mice and adjuvant arthritis in rats. In addition, this compound inhibited increased vascular permeability in rat skin induced by leukotriene D4 and platelet activating factor-induced pleurisy in rats in a dose-dependent manner. These results indicate that DS-4574 inhibited type III allergic reactions and some inflammatory reactions. Therefore, DS-4574 could be useful in the treatment of allergic diseases such as asthma.

Inhibitory effect of DS-4574 on leukotriene- or antigen-induced bronchoconstriction in guinea pigs.

We studied the leukotriene (LT) antagonistic activity of DS-4574 in vivo and the inhibitory effect of this compound on antigen-induced bronchoconstriction in actively sensitized guinea pigs. Bronchoconstriction induced by LTD4 was inhibited by intravenous and oral treatment with DS-4574 in a dose-dependent manner. Orally administered DS-4574 was also able to inhibit the bronchoconstriction mediated by intravenous administration of LTC4 and E4 and that by endogenous LTs. The inhibitory effect of DS-4574 showed similar potency to those of FPL-55712 and LY171883. In contrast, histamine-, acetylcholine- or 5-hydroxytryptamine-induced bronchoconstriction was not significantly affected by DS-4574. Moreover, DS-4574 given orally or intravenously inhibited antigen-induced bronchoconstriction in actively sensitized guinea pigs and this compound prevented antigen-induced mediator release from actively sensitized guinea-pig lung fragments. The anti-asthmatic effect of this compound appears to be associated with LT antagonism and inhibition of the release of chemical mediators. This study therefore shows DS-4574 to have orally effective LT antagonistic and anti-asthmatic activities. This compound may prove useful in the treatment of bronchial asthma.

Three-dimensional structure of soybean beta-amylase determined at 3.0 A resolution: preliminary chain tracing of the complex with alpha-cyclodextrin.

The three-dimensional structure of a complex of soybean beta-amylase [EC 3.2.1.2] with an inhibitor, alpha-cyclodextrin, has been determined at 3.0 A resolution by X-ray diffraction analysis. Preliminary chain tracing showed that the enzyme folded into large and small domains. The large domain has a (beta alpha)8 super-secondary structure, while the smaller one is formed from two long loops extending from the beta 3 and beta 4 strands of the (beta alpha)8 structure. The interface of the two domains together with shorter loops from the (beta alpha)8 structure form a deep cleft, in which alpha-cyclodextrin binds slightly away from the center. Two maltose molecules also bind in the cleft. One shares a binding site with alpha-cyclodextrin and the other is situated more deeply in the cleft.

Synthesis and antiallergy activity of [1,3,4]thiadiazolo[3,2-a]-1,2,3-triazolo[4,5-d]pyrimidin-9(3H)-one derivatives. II. 6-Alkyl- and 6-cycloalkylalkyl derivatives.

A series of 6-alkyl- or 6-(cycloalkylalkyl)-[1,3,4]thiadiazolo[3,2- a]-1,2,3-triazolo[4,5-d]pyrimidin-9(3H)-ones 1b--o was synthesized from the corresponding 1,3,4-thiadiazol-5-amines 3b--o and the antiallergic activities of the products were evaluated. Among the compounds 6-(2-cyclohexylethyl)- [1,3,4]thiadiazolo[3,2-a]-1,2,3-triazolo[4,5-d]pyrimidin-9(3H)-one 1h, whose X-ray crystallographic stereostructure is shown, was found to be a promising new antiallergic agent, which has low toxicity and dual activity as a leukotriene D4 receptor antagonist and as an orally active mast cell stabilizer.

The primary structure of omega-amino acid:pyruvate aminotransferase.

The complete amino acid sequence of bacterial omega-amino acid:pyruvate aminotransferase (omega-APT) was determined from its primary structure. The enzyme protein was fragmented by CNBr cleavage, trypsin, and Staphylococcus aureus V8 digestions. The peptides were purified and sequenced by Edman degradation. omega-ATP is composed of four identical subunits of 449 amino acids each. The calculated molecular weight of the enzyme subunit is 48,738 and that of the enzyme tetramer is 194,952. No disulfide bonds or bound sugar molecules were found in the enzyme structure, although 6 cysteine residues were determined per enzyme subunit. Sequence homologies were found between an omega-aminotransferase, i.e. mammalian and yeast ornithine delta-aminotransferases, fungal gamma-aminobutyrate aminotransferase and 7,8-diaminoperalgonate aminotransferase, and 2,2-dialkylglycine decarboxylase. The enzyme structure is not homologous to those of aspartate aminotransferases (AspATs) including the enzymes of Escherichia coli and Sufolobus salfactaricus, though significant homology in the three-dimensional structures around the cofactor binding site has been found between omega-APT and AspATs (Watanabe, N., Sakabe, K., Sakabe, N., Higashi, T., Sasaki, K., Aibara, S., Morita, Y., Yonaha, K., Toyama, S., and Fukutani, H. (1989) J. Biochem. 105, 1-3).

Synthesis and antiallergy activity of [1,3,4]thiadiazolo[3,2-a]-1,2,3-triazolo[4,5-d]pyrimidin-9 (3H)-one derivatives. I.

A series of 6-substituted [1,3,4]thiadiazolo[3,2-a]-1,2,3-triazolo[4,5-d]pyrimidin-9(3H)-one derivatives 4a--z were synthesized from 5-substituted 1,3,4-thiadiazol-2-amines 5 by the following consecutive reactions: pyrimidine ring closure with bis(2,4,6-trichlorophenyl) malonate, nitration, chlorination, amination, hydrogenation and diazotization. The structure of 4 was confirmed by an alternate synthesis of 4, involving reaction of 5-substituted 2-azido-1,3,4-thiadiazole 13 with ethyl cyanoacetate, followed by the Dimroth rearrangement and ring closure. The antiallergic activities (anti-passive peritoneal anaphylaxis, anti-passive cutaneous anaphylaxis and anti-slow reacting substance of anaphylaxis activities) of the products were evaluated.

Antiallergic activity of 6-(2-cyclohexylethyl)-[1,3,4]thiadiazolo- [3,2-a]-1,2,3-triazolo-[4,5-d]pyrimidin-9(3H)-one (DS-4574) in rats.

The antiallergic activity of DS-4574 was evaluated in several commonly used rat models for allergic diseases. In passive cutaneous anaphylaxis, DS-4574 given intravenously and orally induced dose-dependent inhibition with ID50 values of 0.55 and 2.8 mg/kg, respectively. In contrast, this compound had no antagonistic activity against the histamine- and serotonin-induced cutaneous vascular permeability. In lung anaphylaxis, DS-4574 inhibited pulmonary function changes induced by the antigen in a dose-dependent manner when it was given intravenously and orally, the ID50 values being 0.04 and 0.89 mg/kg, respectively. DS-4574 also inhibited antigen-induced histamine and leukotriene release in passive peritoneal anaphylaxis following oral administration. In addition, this compound prevented antigen-induced histamine release in passively sensitized mast cells in vitro. These potent activities of DS-4574 in in vivo and in vitro models of immediate-type hypersensitivity reactions suggest that this compound could be useful in the treatment of allergic diseases including asthma.

Antagonistic action of DS-4574 against leukotrienes in guinea-pig smooth muscle.

We investigated the effect of a new antiallergic agent, DS-4574, on the guinea-pig smooth muscle contractions induced by leukotriene C4, D4 and E4 (LTC4, D4 and E4) in vitro. In isolated guinea-pig ileum, DS-4574 antagonized the contraction induced by LTC4, LTD4 and LTE4 with IC50 values of 3.5 x 10(-7), 2.0 x 10(-7) and 2.6 x 10(-7) M, respectively. In contrast, at 10(-4) M this compound inhibited the contractions induced by histamine, acetylcholine, 5-hydroxytryptamine, bradykinin and prostaglandin F2 alpha by less than 50%. In isolated tracheal strip preparations of guinea-pigs, DS-4574 produced a parallel concentration-dependent rightward shift of the leukotriene concentration-response curves without affecting the maximal response. The dissociation constant of DS-4574, obtained against LTC4, LTD4 and LTE4, was 3.07 +/- 0.47 x 10(-8), 1.81 +/- 0.36 x 10(-8) and 7.30 +/- 3.40 x 10(-8) M, respectively. The slopes of Schild plots for DS-4574 against leukotrienes did not differ significantly from unity. In the presence of an inhibitor of the metabolism of LTC4 to LTD4, about 100 times higher concentrations of DS-4574 were required to antagonize LTC4-induced contractions. Moreover, DS-4574 competed with the [3H]LTD4-, [3H]LTE4- and [3H]LTC4-specific binding to the receptor in guinea-pig lung membranes with Ki values of 7.2 x 10(-7), 4.5 x 10(-7) and 3.9 x 10(-5) M, respectively. The present data suggest that DS-4574 is a selective and competitive leukotriene antagonist. When the leukotriene antagonism by DS-4574 is confirmed in other species, it might be useful in a variety of diseases associated with excessive production of leukotrienes.

A Lipoxygenase Pathway Is Activated in Rice after Infection with the Rice Blast Fungus Magnaporthe grisea.

Lipoxygenase (LOX) and lipid hydroperoxide-decomposing activity (LHDA) markedly increased in the fifth leaves of rice (Oryza sativa cv Aichiasahi) after infection with the rice blast fungus, Magnaporthe grisea. The increases in the enzyme activities were significantly higher in response to infection with an incompatible strain (race 131) compared with infection with a compatible strain (race 007) of the fungus. Using ion-exchange chromatography, we isolated three LOX activities (leaf LOX-1, -2, -3) from both uninoculated and infected leaves. The activity of leaf LOX-3, in particular, increased in the incompatible race-infected leaves. The leaf LOX-3 had a pH optimum of 5.0 and produced preferentially 13-l-hydroperoxy-9,11 (Z,E)-octadecadienoic acid (13-HPODD) from linoleic acid. 13-HPODD and 13-l-hydroxy-9,11 (Z,E)-octadecadienoic acid, one of the reaction products from 13-HPODD by LHDA, were highly inhibitory to the germination of conidia of the fungus. The present study provides correlative evidence for important roles of LOX and LHDA in the resistance response of rice against the blast fungus.

Three-dimensional structure of Cu,Zn-superoxide dismutase from spinach at 2.0 A resolution.

The three-dimensional structure of Cu,Zn-superoxide dismutase from spinach leaves has been determined by X-ray crystal structure analysis. The atomic coordinates were refined at 2.0 A resolution using the Hendrickson and Konnert program for stereochemically restrained refinement against structure factors, which allowed the use of non-crystallographic symmetry. The crystallographic residual error for the refined model was 24.9%, with a root mean square deviation of 0.03 A from the ideal bond length and an average atomic temperature factor of 9.6 A. A dimeric molecule of the enzyme is comprised of two identical subunits related by a non-crystallographic 2-fold axis. Each subunit of 154 amino acid residues is composed primarily of eight anti-parallel beta-strands that form a flattened cylinder, plus three external loops. The main-chain hydrogen bonds primarily link the beta-strands. The overall structure of this enzyme is quite similar to that of the bovine dismutase except for some parts. The single disulfide bridge (Cys57-Cys146) and the salt bridge (Arg79-Asp101) may stabilize the loop regions of the structure. The Cu2+ and Zn2+ ions in the active site lie 6.1 A apart at the bottom of the long channel. The Cu2+ ligands (ND1 of His-46, and NE2 of His-48, -63, and -120) show an uneven tetrahedral distortion from a square plane. The Zn2+ ligands (ND1 of His-63, -71, and -80 and OD1 of Asp-83) show an almost tetrahedral geometry. The imidazole ring of His-63 forms a bridge between the Cu2+ and Zn2+ ions.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effect of midaglizole on alpha adrenoceptor agonist-induced contractions of canine tracheal smooth muscle.

To determine why midaglizole is effective in some patients with severe asthma, we investigated the inhibitory effects of midaglizole, prazosin or yohimbine on the BHT 920-, phenylephrine-, or noradrenaline-induced contractions of canine tracheal smooth muscle. After pretreatment with atropine (10(-6) M) and propranolol (10(-6) M) and precontraction with serotonin (3 x 10(-7) M), the tracheal muscle showed contractile responses to the exogenous administration of both alpha 1 and alpha 2 adrenoceptor agonists. Every alpha antagonist inhibited these agonist-induced contractions. Inhibitory activity of midaglizole (10(-4) M) for the alpha agonists was BHT-920 greater than noradrenaline greater than or equal to phenylephrine, while that of prazosin (3 x 10(-6) M) was phenylephrine greater than noradrenaline greater than BHT-920. Moreover, yohimbine completely inhibited the contractions at the lower concentration of 3 x 10(-7) M than that of other two antagonists. Our findings demonstrate that midaglizole dose-dependently inhibits airway contractions induced by alpha adrenoceptor agonists.

Crystal structure analysis of omega-amino acid:pyruvate aminotransferase with a newly developed Weissenberg camera and an imaging plate using synchrotron radiation.

The three-dimensional structure of omega-amino acid:pyruvate aminotransferase from Pseudomonas sp. F-126, an isologous alpha 4 tetramer containing pyridoxal 5'-phosphate (PLP) as a cofactor, has been determined at 2.0 A resolution. The diffraction data were collected with a newly developed Weissenberg camera with a Fuji Imaging Plate, using synchrotron radiation. The mean figure-of-merit was 0.57. The subunit is rich in secondary structure and comprises two domains. PLP is located in the large domain. The high homology in the secondary structure between this enzyme and aspartate aminotransferase strongly indicates that these two types of enzymes have evolved from a common ancestor.

Purification, crystallization, and characterization of peroxidase from Coprinus cinereus.

Peroxidase (donor: H2O2 oxidoreductase [EC 1.11.1.7]) was purified from a culture broth of an inkcap Basidiomycete, Coprinus cinereus S.F. Gray. A single component containing a low amount of carbohydrate was isolated by affinity chromatography on concanavalin A-Sepharose and crystallized from ammonium sulfate solution. The enzyme is an acidic protein (pI 3.5) and consists of a single polypeptide chain having the molecular weight of 41,600 daltons. The enzyme contains one protohemin per molecule and exhibits the characteristic absorption, circular dichroism, and magnetic circular dichroism spectra of a heme-protein. The Coprinus peroxidase forms two characteristic intermediate compounds, I and II, and the rate constants for hydrogen peroxide and guaiacol had similar values to those for higher plant peroxidases. The ferric enzyme formed a cyanide compound with a dissociation constant similar to those for higher plant enzyme, but the dissociation constant of the ferrous enzyme-cyanide was large. The chemical composition of Coprinus peroxidase showed 381 amino acid residues, 1 glucosamine, 3 true sugars, 3 calcium, and 1 non-heme iron other than 1 protohemin. The secondary structure of the fungal enzyme was very similar to that of horseradish peroxidase.