Fractionnement d'une préparation cellulasique de trichoderma viride par chromatographie d'affinité sur cellulose réticulée

4-Thiocellooligosaccharides. Their synthesis and use as ligands for the separation of cellobiohydrolases of Trichoderma reesei by affinity chromatography

4-Aminophenyl 1,4-dithio-beta-cellobioside (6) was obtained by treatment of methyl 2,3,6-tri-O-benzoyl-4-O-triflyl-alpha-D-galactopyranoside with the sodium salt of 1-thio-beta-D-glucopyranose, followed by acetolysis and glycosylation of the corresponding bromide with 4-aminobenzenethiol and subsequent deacylation. A similar synthesis starting with the 1-thiolate of 1,4-dithio-beta-cellobiose led to the trisaccharide 4-aminophenyl 1,4,4'-trithiocellotrioside (16). The 4-acetamidophenyl di- and tri-thiocellooligosaccharides were found to be excellent competitive inhibitors of the hydrolysis of 4-methylumbelliferyl beta-lactoside with respective Ki values of 25 and 6.5 mM. The two 4-aminophenyl oligosaccharides 6 and 16 were coupled to CH-Sepharose 4B, and the affinity gels were used for the purification of cellobiohydrolases from a crude commercial cellulolytic extract of T. reesei. Cellobiohydrolases I or II were selectively desorbed from gels bearing ligands 6 and 16.

Regulatory aspects of cellulase biosynthesis and secretion

The cellulase enzyme system consists of cellobiohydrolase, endoglucanase, and beta-glucosidase and has been extensively studied with respect to its biosynthesis, properties, mode of action, application, and, most recently, secretion mechanisms. A knowledge of the factors governing the biosynthesis and secretion of these enzymes at the molecular level will be useful in maximizing enzyme productivity in extracellular fluid. Among other topics, the regulatory effects of sorbose (a noninducing sugar which is not a product of cellulose hydrolysis) on cellulase synthesis and release are described. Cellulase genes have recently been cloned into a number of microorganisms with a view to understanding the gene structure and expression and to obtaining the enzyme components in pure form. The factors governing biosynthesis and secretion of cellulases in recombinant cells are also discussed. Cellulases are known to be glycoproteins, therefore, the role of O- and N-linked glycosylation on enzyme stability and secretion is also detailed.

Fractionation of the cellulolytic enzymes produced by a species of Monilia; purification and properties of an extracellular beta-D-glucosidase

Extracellular cellulolytic enzymes produced by a species of Monilia could be fractionated by chromatography on SP-Sephadex, Con A-Sepharose, and cellobiose-Sepharose. These methods did not separate the beta-D-glucosidases (beta-D-glucoside glucohydrolases, EC 3.2.1.21) from the cellulases and xylanases within a single purification step. Fractionation by isoelectric focusing on a flat-bed granulated gel gave all of the beta-D-glucosidase activity in a single zone isoelectric at pH 8-9. The beta-D-glucosidase could be further purified to homogeneity by column isoelectric focusing at pH 8.0-10.5, and gel filtration on Biogel P-100. The purified beta-D-glucosidase showed optimal activity at pH 4-5 and 50 degrees, was isoelectric at pH 8.87, and had a molecular weight of 46,600. SDS-Polyacrylamide-gel electrophoresis demonstrated that the beta-D-glucosidase was not dissociated into subunits and, hence, consisted of a single polypeptide chain. The enzyme is considered a glycoprotein, as it binds to Con A-Sepharose. The beta-D-glucosidase hydrolyzed (1----2)-, (1----4)-, and (1----6)-beta-D-glucosidic linkages but not cellulose. Nitrophenyl beta-D-glucopyranosides and beta-D-xylopyranosides were also degraded. The beta-D-glucosidase was competitively inhibited by D-glucose (Ki 0.67 mM).