Identification of the active site nucleophile in the thermostable beta-glycosidase from the archaeon Sulfolobus solfataricus expressed in Escherichia coli

Sulfolobus solfataricus beta-glycosidase expressed in Escherichia coli was fully inactivated at 65 degrees C, according to pseudo-first-order kinetics, by [3H]conduritol B epoxide (DL-1,2 anhydro-myo-inositol) synthesized as the active site directed inhibitor by a slight modification of Legler's procedure [Legler, G. (1977) Methods Enzymol. 46, 368-381]. The determination of kinetic constants for the inactivation showed that the process took place through the formation of a stabilized inhibitor-enzyme intermediate. Inactivation and reactivation studies suggested that the inhibitor-enzyme intermediate complex was formed more rapidly and hydrolyzed at a lower rate than it was for other glycosidases. Moreover, the stoichiometry of the binding, determined by electrospray mass spectrometric analysis, revealed that one molecule of the inhibitor was covalently bound to each enzyme subunit. The binding site for [3H]conduritol B epoxide was identified by the isolation and partial sequence analysis of the radioactive peptide obtained by cyanogen bromide and pepsin digests. Electrospray tandem mass analysis of the labeled peptide showed that the inhibitor was covalently bound to E387. This result, in agreement with data obtained from sequence alignments of S. solfataricus beta-glycosidase with other gluco- and galactosidases of the glycosyl hydrolase family 1 [Henrissat, B. (1991) Biochem. J. 280, 309-316], indicates that the conserved E387 is the nucleophilic amino acid residue in the active site of the enzyme.

Light and electron microscopy study of carbohydrate antigens found in the electron-lucent layer of Pneumocystis carinii cysts

The localization and biochemical nature of antigens found in the electron-lucent layer (ELL) of Pneumocystis carinii cysts using polyclonal rabbit antibodies are described. These antigens, specific for the cystic stages of the parasite, were shared by organisms from different hosts, suggesting that they represent functionally important components of the cyst cell wall. The binding sites were situated on an interwoven net of fibrils in the ELL produced by mild to strong proteolysis. Degradation of this residue by glucanase and chitinase confirms that this layer contains branched glucan and chitin. In contrast, the prompt susceptibility of the polysaccharide-rich ELL to proteolysis reveals that proteins are also relevant in building up the cyst-wall glucan skeleton. It is therefore concluded that the formation of the Pneumocystis cyst wall shows differences to the typical fungal cell-wall architecture. The taxonomical debate regarding this unique protist is ongoing, and consideration of these immunological and morphological findings may be useful for the study of the biology and phylogeny of Pneumocystis.

ENZYMATIC HYDROLYSIS OF YEAST CELL WALLS. I. ISOLATION OF WALL-DECOMPOSING ORGANISMS AND SEPARATION AND PURIFICATION OF LYTIC ENZYMES

Tanaka, Hirosato (University of California, Davis), and Herman J. Phaff. Enzymatic hydrolysis of yeast cell walls. I. Isolation of wall-decomposing organisms and separation and purification of lytic enzymes. J. Bacteriol. 89:1570-1580. 1965.-A number of microorganisms, able to decompose and grow on yeast cell walls, were isolated from soil. These isolates demonstrated various types of attack on yeast walls. A bacterium, identified as Bacillus circulans, and a species of Streptomyces produced clear, lysed zones when grown on an agar medium containing baker's yeast cell walls. The streptomycete formed glucanase, mannanase, and protease, but B. circulans produced only glucanases. Purified mannan could be prepared from the culture fluid of B. circulans grown on baker's yeast cell walls. In a liquid, mineral medium, extracellular lytic enzyme production by B. circulans was optimal after 3 days of aerobic growth at 30 C with 0.5% baker's yeast cell walls as the carbon source. Twelve other carbon sources were ineffective as inducers. Among a number of polysaccharides tested, the crude enzymes of B. circulans hydrolyzed only beta-1-->3 glucan (laminarin) and beta-1-->6 glucan (pustulan), both by a random mechanism, to a mixture of dimer and glucose. The beta-1-->3 and beta-1-->6 glucanases were separated from each other by diethylaminoethyl cellulose column chromatography. Water-soluble oat glucan, which contains in the linear chain both beta-1-->3 and beta-1-->4 bonds, was also hydrolyzed by the bacterial beta-1-->3 glucanase. The products of this reaction indicated that this enzyme hydrolyzes beta-1-->3 or beta-1-->4 glucosidic linkages, provided the beta-glucopyranosyl units composing these bonds are substituted in the 3 position by another glucose unit.

AN INDUCIBLE SYSTEM FOR THE HYDROLYSIS AND TRANSPORT OF BETA-GLUCOSIDES IN YEAST. I. CHARACTERISTICS OF THE BETA-GLUCOSIDASE ACTIVITY OF INTACT AND OF LYSED CELLS

A strain of bakers' yeast was isolated which could utilize cellobiose and other β-D-glucosides quantitatively as carbon and energy sources for growth. Cellobiose-grown cells contained a largely cryptic enzyme active against the chromogenic substrate p-nitrophenyl-β-D-glucoside. The patent (intact cell) activity of such cells was inhibited by azide and, competitively, by cellobiose; neither agent inhibited the β-glucosidase activity of lysed cells or of extracts. The enzyme induced by growth in cellobiose medium had no affinity for cellobiose as either substrate or inhibitor; its substrate specificity classifies it as an aryl-β-glucosidase. It was concluded that growth in cellobiose also induced the formation of a stereospecific and energy-dependent system whose function determined the rate at which intact cells could hydrolyze substrates of the intracellular β-glucosidase.

RAT-KIDNEY LYSOSOMES: ISOLATION AND PROPERTIES

1. The activities of lysosomal enzymes in the cortexes and medullas and the principal subcellular fractions of rat kidney were measured. 2. A method is described for the isolation of rat-kidney lysosomes and a detailed analysis of the enzymic composition of the lysosomes is reported. Enzyme analysis of the other principal subcellular fractions is included for comparison. 3. Studies of the distribution of alpha-glucosidase showed that the lysosomal fraction contained only 10% of the total enzyme activity. The microsomal fraction contained most of the particulate alpha-glucosidase. Lysozyme was concentrated mainly in the lysosomal fraction with only small amounts present in the microsomal fraction. Lysosomal alpha-glucosidase had optimum pH5 whereas the microsomal form had optimum pH6. Both lysosomal and microsomal lysozyme had optimum pH6.2. 4. The stability of lysosomal suspensions was studied. Incubation at 37 degrees and pH7 resulted in first an increased availability of enzymes without parallel release of enzyme. This was followed by a second stage during which the availability of enzymes was closely related to the release of enzymes. These changes were closely paralleled by changes in light-scattering properties of lysosomes. 5. The latent nature of the alpha-glucosidase and lysozyme of intact kidney lysosomes was demonstrated by their graded and parallel release with other typical lysosomal enzymes. 6. Isolated lysosomes were unstable at pH values lower than 5, most stable at pH6-7 and less stable at pH 8-9. Lysosomes were not disrupted when the osmolarity of the suspending medium was decreased from 0.6m to 0.25m. 7. The discussion compares the properties and composition of kidney lysosomes, liver lysosomes and the granules of macrophages. 8. The possible origin of the lysozyme in kidney lysosomes by reabsorption of the lysozyme in blood is discussed.

STUDIES ON A GLYCOPEPTIDE FROM OVALBUMIN

1. The structure of the carbohydrate component of the glycopeptide isolated from the proteolytic digest of ovalbumin has been investigated by chemical and enzymic methods. 2. The results are consistent with the presence of a single carbohydrate prosthetic group, linked through its reducing end group to the peptide chain. 3. Further, all the 2-amino-2-deoxy-d-glucose units appear to be in the N-acylated form, the phenolic hydroxyl group of tyrosine is free and the omega-carboxyl group of aspartic acid is substituted. 4. The carbohydrate component has a branched-chain structure, the two non-reducing ends being terminated by a d-mannopyranosyl and a 2-acetamido-2-deoxy-d-glucopyranosyl residue respectively. 5. The terminal d-mannopyranosyl unit is probably linked through at least one other d-mannopyranosyl residue to the remainder of the carbohydrate.

STUDIES ON CARBOHYDRATE-METABOLIZING ENZYMES. THE HYDROLYSIS OF ALPHA-GLUCOSIDES, INCLUDING NIGEROSE, BY EXTRACTS OF ALFALFA AND OTHER HIGHER PLANTS

1. Enzyme preparations from 11 plant sources, from yeast and from the protozoan Tetrahymena pyriformis show nigerase activity, which, in most preparations, was 70-90% of that towards maltose. 2. These enzyme preparations also hydrolysed isomaltose, but there was a wide variation in relative maltase to isomaltase activity. 3. The maltase and nigerase activities of alfalfa and tomato preparations could not be differentiated by heat inactivation or inhibitor methods. However, with turanose used as a competitive inhibitor, evidence suggesting that maltose and nigerose are hydrolysed at different catalytically active sites in the alfalfa preparation was obtained. 4. It is probable that the alfalfa alpha-glucosidase exists as a mixture of isoenzymes.

BETA-GLUCOSIDASE SYSTEM OF NEUROSPORA CRASSA. I. BETA-GLUCOSIDASE AND CELLULASE ACTIVITIES OF MUTANT AND WILD-TYPE STRAINS

Eberhart, Bruce (University of North Carolina, Greensboro), David F. Cross, and Lewis R. Chase. beta-Glucosidase system of Neuspora crassa. I. beta-Glucosidase and cellulose activities of mutant and wild-type strains. J. Bacteriol. 87:761-770. 1964.-A mutant strain, gluc-1, of Neurospora crassa was isolated and characterized by its low level of beta-glucosidase activity. The mutant was selected by testing irradiated colonies for extracellular beta-glucosidase activity. Strains containing the gluc-1 gene were also visibly detected by their reduced ability to destroy esculin in their growth media. The mutant strain grew at wild-type rates with cellobiose or carboxymethylcellulose as carbon sources. This auxotrophic similarity with wild type is explained by the presence of at least two beta-glucosidases (and possibly two cellulases) in Neurospora that act complementarily. The thermolabile beta-glucosidase was destroyed after 1 min of incubation at 60 C. This enzyme was present in mycelia but absent in conidial extracts. A second beta-glucosidase that is comparatively stable at 60 C was present in both mycelia and conidia. A partial separation of these enzymes was achieved with ammonium fractionation of mycelial extracts of gluc-1 and wild-type strains. Thermolabile beta-glucosidase and cellulase activity appear not to be affected by the gluc-1 mutation, whereas the thermostable glucosidase is greatly reduced in gluc-1 strains.

Molecular identity and cellular distribution of advanced glycation endproduct receptors: relationship of p60 to OST-48 and p90 to 80K-H membrane proteins

Advanced glycation endproducts (AGEs) are derivatives of nonenzymatic reactions between sugars and protein or lipids, and together with AGE-specific receptors are involved in numerous pathogenic processes associated with aging and hyperglycemia. Two of the known AGE-binding proteins isolated from rat liver membranes, p60 and p90, have been partially sequenced. We now report that the N-terminal sequence of p60 exhibits 95% identity to OST-48, a 48-kDa member of the oligosaccharyltransferase complex found in microsomal membranes, while sequence analysis of p90 revealed 73% and 85% identity to the N-terminal and internal sequences, respectively, of human 80K-H, a 80- to 87-kDa protein substrate for protein kinase C. AGE-ligand and Western analyses of purified oligosaccharyltransferase complex, enriched rough endoplasmic reticulum, smooth endoplasmic reticulum, and plasma membranes from rat liver or RAW 264.7 macrophages yielded a single protein of approximately 50 kDa recognized by both anti-p60 and anti-OST-48 antibodies, and also exhibited AGE-specific binding. Immunoprecipitated OST-48 from rat rough endoplasmic reticulum fractions exhibited both AGE binding and immunoreactivity to an anti-p60 antibody. Immune IgG raised to recombinant OST-48 and 80K-H inhibited binding of AGE-bovine serum albumin to cell membranes in a dose-dependent manner. Immunostaining and flow cytometry demonstrated the surface expression of OST-48 and 80K-H on numerous cell types and tissues, including mononuclear, endothelial, renal, and brain neuronal and glial cells. We conclude that the AGE receptor components p60 and p90 are identical to OST-48, and 80K-H, respectively, and that they together contribute to the processing of AGEs from extra- and intracellular compartments and in the cellular responses associated with these pathogenic substances.

Identification of p90, a prominent tyrosine-phosphorylated protein in fibroblast growth factor-stimulated cells, as 80K-H

Tyrosine phosphorylation of cellular proteins occurs rapidly upon treatment of fibroblasts with acidic or basic fibroblast growth factors (aFGF, bFGF), suggesting a role for protein phosphorylation in the FGF signaling pathway. Stimulation of Swiss 3T3 cells and MRC-5 fibroblasts with bFGF results in the tyrosine phosphorylation of several proteins, of which the most prominent has been designated as p90. The phosphorylation of p90 is observed within 30 s of treating the cells with FGF but not with other growth factors. Microsequencing of p90 resolved on two-dimensional polyacrylamide gel electrophoresis indicated an N-terminal amino acid sequence which corresponded to a protein previously named as 80K-H. Polyclonal antibodies raised against the predicted C terminus of 80K-H recognized p90 on all Western blots. p90 was found to bind specifically to GRB-2-glutathione S-transferase fusion protein and to be immunoreactive with 80K-H antibody. In addition, anti-phosphotyrosine antibodies immunoprecipitated 80K-H from cell lysates of FGF-stimulated but not from control fibroblasts. The biological function of 80K-H is yet unknown. However, from this study and a previous observation of the obligatory dependence of p90 phosphorylation on FGF receptor occupation, it appears that 80K-H is involved in FGF signaling.

A 3-Mb region for the familial hemiplegic migraine locus on 19p13.1-p13.2: exclusion of PRKCSH as a candidate gene. Dutch Migraine Genetic Research Group

Familial hemiplegic migraine (FHM) is an autosomal domianant subtype of migraine with attacks, associated with transient episodes of hemiparesis. One of the genes for FHM has been assigned to chromosome 19p13. Detailed analysis of critical recombinants from two different chromosome 19-linked FHM families, using new markers indicated a 6-cM candidate region on 19p13.1-p13.2 flanked by loci D19S394 and D19S226. Another paroxysmal neurological disorder, episodic ataxia type 2 (EA-2), has also been linked to the same chromosomal region. Most of the interval was completely covered by YAC and cosmid contigs; the physical map yielded approximately 3 Mb encompassing several genes including the protein kinase substrate 80K-H (PRKCSH) gene. Since PRKCSH is involved in neuronal signal transduction, it was considered to be an FHM candidate gene. The genomic structure of this gene was established and mutation analysis for all exon and flanking intron sequences was performed in FHM- and EA-2-affected individuals. Five polymorphisms were identified, including a trinucleotide repeat length variation in the coding sequence. However, no potential disease causing mutation was found and therefore the PRKCSH gene can be excluded for both FHM and EA-2.

[Effect of enzyme mixtures in broiler diets of barley, rye or wheat]

In three trials with a total of 4120 male and female broilers, kept on floor or in cages maize has been partly replaced by barley, rye or triticale and different combinations of enzymes were fed. The supplementation of cellulases with mainly glucanase in barley based diets has had no significant influence on growth performance. In case of diets with 20% rye the addition of cellulases with mainly hemicellulases resulted in 5% higher live weight gains and a better feed efficiency (5%) on average of two trials. The negative influence of rye feeding on excrement constitution was lowered and the dry matter content of excrements increased by 1.3%. In diets based on triticale the growth performance of broilers was insignificantly better. The addition of enzymes did not influence the proportion of different body fractions as well as the crude nutrient content of edible carcass.