The action pattern of Penicillium lilacinum dextranase

Products Released from Structurally Different Dextrans by Bacterial and Fungal Dextranases

Dextran hydrolysis by dextranases is applied in the sugar industry and the medical sector, but it also has a high potential for use in structural analysis of dextrans. However, dextranases are produced by several organisms and thus differ in their properties. The aim of this study was to comparatively investigate the product patterns obtained from the incubation of linear as well as O3- and O4-branched dextrans with different dextranases. For this purpose, genes encoding for dextranases from Bacteroides thetaiotaomicron and Streptococcus salivarius were cloned and heterologously expressed in Escherichia coli. The two recombinant enzymes as well as two commercial dextranases from Chaetomium sp. and Penicillium sp. were subsequently used to hydrolyze structurally different dextrans. The hydrolysis products were investigated in detail by HPAEC-PAD. For dextranases from Chaetomium sp., Penicillium sp., and Bacteroides thetaiotaomicron, isomaltose was the end product of the hydrolysis from linear dextrans, whereas Penicillium sp. dextranase led to isomaltose and isomaltotetraose. In addition, the latter enzyme also catalyzed a disproportionation reaction when incubated with isomaltotriose. For O3- and O4-branched dextrans, the fungal dextranases yielded significantly different oligosaccharide patterns than the bacterial enzymes. Overall, the product patterns can be adjusted by choosing the correct enzyme as well as a defined enzyme activity.

Microbial dextran-hydrolyzing enzymes: fundamentals and applications

Dextran is a chemically and physically complex polymer, breakdown of which is carried out by a variety of endo- and exodextranases. Enzymes in many groups can be classified as dextranases according to function: such enzymes include dextranhydrolases, glucodextranases, exoisomaltohydrolases, exoisomaltotriohydrases, and branched-dextran exo-1,2-alpha-glucosidases. Cycloisomalto-oligosaccharide glucanotransferase does not formally belong to the dextranases even though its side reaction produces hydrolyzed dextrans. A new classification system for glycosylhydrolases and glycosyltransferases, which is based on amino acid sequence similarities, divides the dextranases into five families. However, this classification is still incomplete since sequence information is missing for many of the enzymes that have been biochemically characterized as dextranases. Dextran-degrading enzymes have been isolated from a wide range of microorganisms. The major characteristics of these enzymes, the methods for analyzing their activities and biological roles, analysis of primary sequence data, and three-dimensional structures of dextranases have been dealt with in this review. Dextranases are promising for future use in various scientific and biotechnological applications.

Purification and mode of action of an alkali-resistant endo-1, 4-beta-glucanase from Bacillus pumilus

Alkaline endo-1,4-beta-d-glucanase was secreted by Bacillus pumilus grown in submerged culture on a combination of oat spelt xylan and corn starch as carbon sources. The enzyme was purified to homogeneity by Sephacryl S-200 and Q-Sepharose column chromatography. The protein corresponded to molecular mass and pI values of 67 kDa and 3.7, respectively. The enzyme was optimally active at pH 7.0-8.0 and 60 degrees C and retained 50% of its optimum activity at pH 12. The most notable characteristic of the endoglucanase was its high stability up to pH 12 for 20 h at 30 degrees C. The enzyme hydrolyzed carboxymethylcellulose (CMC) and cello-oligosaccharides but was inactive on cellobiose, cellotriose, Avicel, xylan, 4-nitrophenyl-beta-d-glucoside, 4-nitrophenyl-beta-d-cellobioside, and 4-nitrophenyl-beta-d-xyloside. Analysis of reaction mixtures by HPLC revealed that the enzyme produced almost exclusively cellotriose when acted on CMC and appeared to hydrolyze cello-oligosaccharides by successively releasing cellotriose. The use of 4-methylumbelliferyl cello-oligosaccharides and the determination of bond cleavage frequency revealed that the enzyme preferentially hydrolyzed the third glycosidic bond adjacent to the glycon. The enzyme mediated a decrease in the viscosity of CMC associated with a release of only small amounts of reducing sugar. The enzyme activity was not inhibited by metal ions, surfactants, and chelating agents used as components of laundry detergents.

Purification and characterisation of a major xylanase with cellulase and transferase activities from Fusarium oxysporum

A major xylanase from Fusarium oxysporum was purified to homogeneity by gel filtration, affinity, and ion-exchange chromatographies. It has a molecular mass of 60.2 kDa and pI of 6.6 and was optimally active at pH 7.4 and at 50 degrees C. The enzyme was stable over the pH range 5.8-8.2 at 40 degrees C for 24 h and lost 45% of its original activity at pH 9.0 under the identical conditions. The enzyme rapidly hydrolysed xylans from oat spelts (husks) and birchwood, but the activities on carboxymethylcellulose (CMC), filter paper, and Avicel were very low. Determination of kcat/Km revealed that the enzyme hydrolysed oat spelts and birchwood xylans, 15-30 times more efficiently than CMC. In a 24 h incubation, at pH 7.0 and 9.0, the enzyme hydrolysed oat spelts and birchwood xylans by 75 and 65%, respectively. However, at pH 7.0, the enzyme released almost equal amounts of xylose and xylobiose from both xylans, whereas at pH 9.0, the concentration of xylobiose was twice as muchi as that of xylose and xylotriose. Xylanase attacked preferentially the internal glycosidic bonds of xylo- and 4-methylumbelliferyl cello-oligosaccharides [MeUmb(Glc)n]. The enzyme catalysed transglycosylation reaction with xylotriose, xylotetraose, and xylopentaose as donors and 4-methylumbelliferyl beta-D-glucoside (MeUmbGlc) as an acceptor.

Study of the mode of action and site-specificity of the endo-(1----4)-beta-D-glucanases of the fungus Penicillium pinophilum with normal, 1-3H-labelled, reduced and chromogenic cello-oligosaccharides

The modes of action of the five major endo-(1----4)-beta-D-glucanases (I, II, III, IV and V) purified from Penicillium pinophilum cellulase were compared by h.p.l.c. analysis, with normal, 1-3H-labelled and reduced cello-oligosaccharides and 4-methylumbelliferyl glycosides as substrates. Significant differences were observed in the preferred site of cleavage even when substrates with the same number of glycosidic bonds were compared. Thus, although endoglucanase I was unable to attack normal cello-oligosaccharides shorter than degree of polymerization 6, it hydrolysed reduced cellopentaose to yield cellotriose and cellobi-itol, and it produced cellotriose and 4-methylumbelliferyl glucoside from 4-methylumbelliferyl cellotetraoside. Endoglucanase IV hydrolysed [1-3H]cellotriose but did not attack either cellotri-itol or 4-methylumbelliferyl cellobioside. These and other anomalous results indicated clearly that modification of the reducing glycosyl residue on the cello-oligosaccharides induces in an apparent change in the mode of action of the endoglucanases. It is suggested that, although cello-oligosaccharide derivatives are useful for differentiating and classifying endoglucanases, conclusions on the mechanism of cellulase action resulting from these measurements should be treated cautiously. Unequivocal information on the mode of endoglucanase action on cello-oligosaccharides was obtained with radiolabelled cello-oligosaccharides of degree of polymerization 3 to 5. Indications that transglycosylation was a property of the endoglucanases were particularly evident with the 4-methylumbelliferyl cello-oligosaccharides. Turnover numbers for hydrolysis of the umbelliferyl cello-oligosaccharides were calculated, and these, along with the other analytical data collected on the products of hydrolysis of the normal, reduced and radiolabelled cello-oligosaccharides, suggested that the various endoglucanases had different roles to play in the overall hydrolysis of cellulose to sugars small enough to be transported through the cell membrane.

Beta-glucosidase from Trichoderma reesei. Substrate-binding region and mode of action on [1-3H]cello-oligosaccharides

To determine the mode of action of the beta-glucosidase from Trichoderma reesei a method was developed for synthesizing [1-3H]cello-oligosaccharides with specific radioactivities of approximately 3000 Ci/mol. The beta-glucosidase removed glucosyl residues from the non-reducing end of the [1-3H]cello-oligosaccharides in a multiple attack mode with little tendency to attack the substrates repetitively. Values of Km were lower for longer cello-oligosaccharides, whereas values of V remained essentially constant. A subsite map, constructed using values of V/Km for the cello-oligosaccharides, showed that the substrate-binding region comprises primarily three subsites.

Streptococcus mutans dextransucrase: functioning of primer dextran and endogenous dextranase in water-soluble and water-insoluble glucan synthesis

The extracellular enzyme activities of Streptococcus mutans 6715 that synthesize glucans from sucrose were concentrated and partially purified by ammonium sulfate precipitation and gel permeation column chromatography. Polyacrylamide gel analysis demonstrated that all of the major proteins precipitated by ammonium sulfate were quantitatively recovered in the high-molecular-weight, enzyme-containing aggregates found in the void volume of the gel column. Anion-exchange column chromatography was used to fractionate the aggregates into preparations, alpha and beta, which produced water-insoluble and water-soluble glucans, respectively. Polyacrylamide gel analysis showed that alpha and beta contained unique proteins and dextransucrase (EC 2.4.1.5) activities. Studies on the time course of glucan synthesis by alpha demonstrated that this enzyme preparation contained dextranase activity, which partially degraded nascent alcohol-insoluble glucan into alcohol-soluble products that were subsequently reincorporated into insoluble product. The beta enzyme preparation contained no detectable dextranase activity. Mixing experiments in the absence of primer dextran demonstrated that the dextranase activity present in alpha could modify glucan production by beta. CsCl density gradient analysis of product glucans demonstrated that exogenous primer dextrans were used as acceptor molecules by both the alpha and beta enzyme preparations, and that water-soluble glucans synthesized by beta could be converted into water-insoluble glucans by alpha. It is proposed that the structural heterogeneity of the native glucans produced from sucrose by S. mutans is a result of the concerted action of glucan-forming dextransucrases and endohydrolytic dextranase activity.