Glycosidases induced in Aspergillus tamarii. Secreted α-d-galactosidase and β-d-mannanase

Abstract

An alpha-D-galactosidase (EC 3.2.1.22) and a beta-D-mannanase (EC 3.2.1.78), which were secreted into the growth medium when Aspergillus tamarii was cultivated in the presence of galactomannan, were purified by a procedure including chromatography on hydroxyapatite and DEAE-cellulose columns. Each of these enzymes showed a single protein band, corresponding to their respective activities, on polyacrylamide-gel electrophoresis. Both enzymes were shown to be glycoproteins containing N-acetylglucosamine, mannose and galactose, with molar proportions of 1:6:1.5 for alpha-D-galactosidase and 1:13:8 for beta-D-mannanase. Mr values as determined by polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate and by the electrophoretic method of Hedrick & Smith [(1968) Arch. Biochem. Biophys. 126, 155-164] were 56000 and 53000 respectively. The alpha-D-galactosidase differed markedly from the mycelial forms I and II studied in the preceding paper [Civas, Eberhard, Le Dizet & Petek (1984) Biochem. J. 219, 849-855] with regard to both its kinetic and structural properties.

AspergillusEnzymes Involved in Degradation of Plant Cell Wall Polysaccharides

“…The presence of galactose residues on the mannan backbone significantly hinders the activity of ␤-mannanase (252), but this effect is small if the galactose residues in the vicinity of the cleavage point are all on the same side of the main chain (251). ␤-Mannanases release predominantly mannobiose and mannotriose from mannan, confirming that they are true endohydrolases (4,64,105,306). It has been shown that A. niger ␤-mannanase binds to four mannose residues during catalysis (249).…”

“…The ability of ␤-mannanases to degrade the mannan backbone depends on several factors, such as the number and distribution of the substituents on the backbone and the ratio of glucose to mannose (250). ␤-Mannanase is most active on galactomannans with a low substitution of the backbone (64). The presence of galactose residues on the mannan backbone significantly hinders the activity of ␤-mannanase (252), but this effect is small if the galactose residues in the vicinity of the cleavage point are all on the same side of the main chain (251).…”

“…Galactomannan-degrading enzymes are produced when Aspergillus is grown on milled soybean (59), locust bean gum (4), galactomannan (64), and mannose (270) (1,356) have been reported. Based on the sequences of these genes, the Aspergillus ␤-mannanase and ␤-mannosidases are assigned to glycosidase families 5 and 2, respectively.…”

Three α‐Galactosidase Genes of Trichoderma reesei Cloned by Expression in Yeast

“…Two of these, galactosidases I and I1 isolated from mycelial extracts, are highly active on melibiose but do not attack galactomannan (Civas et al, 19844. The third enzyme, galactosidase 111 isolated from the culture medium, is only slightly active towards melibiose but is able to liberate galactose from manno-oligosaccharides and from polymeric galactomannan (Civas et al, 1984b).…”

“…The capability of some a-galactosidases to release a-galactosyl side groups from galactomannans has also been studied. Enzymes that can act on intact polymeric galactomannan have been isolated from seeds of Cyumopsis tetragonoloba (guar; Bulpin et al, 1990), Phaseolus vulgaris (French bean; Dhar et al, 1994) and Vigna rudiuta (mung bean; Dey, 1984) and from filamentous fungi such as Aspergillus tamarii (Civas et al, 1984b), Aspergillus niger (Adya and Elbein, 1977;Kaneko et al, 1991) and Trichoderma reesei (Zeilinger et al, 1993). Some cx-galactosidases have no activity on galactomannan such as the one described for Mortierella vinacea (Kaneko et al, 1990).…”