Substrate Specificity ofStreptomyces β-Xylanase toward Glucoxylan

The role of the glucuronoxylan carboxyl groups in the action of endoxylanases of three glycoside hydrolase families: A study with two substrate mutants

“…These observations are difficult to be compared with earlier work in which the glucoxylan used as a substrate still could contain nonmodified MeGlcA residues [8,9]. Specific activities of the enzyme toward modified glucuronoxylans had to be determined at much higher enzyme concentration as indicated in Fig.…”

“…For the bacterial CtGH10 xylanase the polysaccharides were dissolved in 0.05 M Tris-HCl A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 8 buffer, pH 6.5, but otherwise treated in the same way. At time intervals 100 µl aliquots of the incubation mixtures were taken for determination of liberated reducing sugars by SomogyiNelson procedure [21] using calibration with xylose.…”

“…partial conversion of MeGlcA side residues to MeGlc (~30%) were obtained by alkaline extraction of in situ reduced hardwood meal [6,7]. A higher conversion of uronic acids to aldoses (~68%) was achieved by reduction of heteroxylans using metal hydrides after activation of the carboxyl group with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide [8]. Glucoxylan prepared in a similar way was tested as a substrate of Erwinia chrysanthemi GH30 xylanase when the mode of action of this enzyme was still not fully understood [9].…”

Glucuronoyl esterases are active on the polymeric substrate methyl esterified glucuronoxylan

“…The discovery of the enzyme called glucuronoyl esterase in the cellulolytic system of the wood rotting fungus Schizophyllum commune using synthetic esters of uronic acids [1] suggested that the enzyme could have important biotechnological implications. There are reports that one of the covalent linkages between hemicellulose and lignin in plant cell walls are ester linkages between 4-O-methyl-D-glucuronic acid (MeGlcA) and lignin alcohols [2][3][4][5][6][7][8][9][10][11][12][13] which could be potential substrates of the esterase. After the genes coding for glucuronoyl esterase were found to be widely distributed in both prokaryotic and eukaryotic microorganisms, a new family of carbohydrate esterases, CE15, was established [14,15].…”

Characterization of the isozymes of glucuronoxylan xylanohydrolase in the presence of a native cell wall substrate

“…Since most of the enzymes are characterized as endo-l,4-/?-xylanases (EC 3.2.1.8) or exo-1 ,4-fl-xylosidase (EC 3.2.1.37) capable of degrading unsubstituted xylans into small fragments represented by xylose oligomers (Tipson and Horton 1976;Gilkes et al 1991), these enzymes are not particularly effective for the degradation and analysis of xylans that comprise the complex structure of cell wall. A Streptomyces p-xylanase has been characterized that hydrolyses xylans with glucuronic acid, glucose and arabinose substitution but since a range of sugar substitutions influences the hydrolysis site, the fragmentation pattern is complex and confounds interpretation for the elucidation of cell wall structures (Yoshida et al 1994). Glucuronxylanase (EC 3.2.1.136) on the other hand has a restricted recognition site governing the point of hydrolysis, but that recognition site is common to many plant cell wall xylans.…”