Purification and characterization of two minor endo-β-1,4-xylanases of Schizophyllum commune

Two minor extracellular endo-β-1,4-xylanases (XynB and XynC, EC 3.2.1.8) were purified from the culture filtrate of Schizophyllum commune grown on cellulose. The molecular mass of enzymes was estimated to be 30.5 kDa for XynB and 30 kDa for XynC according to SDS-PAGE. Both enzymes were acidic, with pI value 2.8 for XynB and 3.6 for XynC. The highest activities were achieved at 50 °C and pH 5.5 and enzymes were stable up to 40 °C in the pH range 5–7. A comparison of hydrolysis products of glucuronoxylan, rhodymenan and acetylxylan showed different mode of action of all three xylanases of S. commune. Known XynA generated products typical for family 11 of glycoside hydrolase – aldopentaouronic acid from glucuronoxylan and isomeric xylotetraose from rhodymenan. XynB released fragments by one xylopyranosyl unit shorter – aldotetraouronic acid MeGlcA1-2Xylβ1-4Xylβ1-4Xyl from glucuronoxylan and isomeric xylotriose from rhodymenan, products usually generated by xylanases from glycoside hydrolase family 10. XynC liberated aldotetraouronic acid Xylβ-1,4-(MeGlcA-1,2-)Xylβ-1,4-Xyl with glucuronoyl unit attached to the middle xylopyranosyl unit from glucuronoxylan and isomeric xylotetraose from rhodymenan. XynC was also able to release xylose from the reducing end of aldotetraouronic acid MeGlcA1-2Xylβ1-4Xylβ1-4Xyl.