Purification, cloning and characterization of two xylanases from Magnaporthe grisea, the rice blast fungus

Magnaporthe grisea, the fungal pathogen that causes rice blast disease, secretes two endo-beta-1,4-D-xylanases (E. C. 3.2.1.8) when grown on rice cell walls as the only carbon source. One of the xylanases, XYN33, is a 33-kD protein on sodium dodecyl sulfate-polyacrylamide gel and accounts for approximately 70% of the endoxylanase activity in the culture filtrate. The second xylanase, XYN22, is a 22-kD protein and accounts for approximately 30% of the xylanase activity. The two proteins were purified, cloned, and sequenced. XYN33 and XYN22 are both basic proteins with calculated isoelectric points of 9.95 and 9.71, respectively. The amino acid sequences of XYN33 and XYN22 are not homologous, but they are similar, respectively, to family F and family G xylanases from other microorganisms. The genes encoding XYN33 and XYN22, designated XYN33 and XYN22, are single-copy in the haploid genome of M. grisea and are expressed when M. grisea is grown on rice cell walls or on oatspelt xylan, but not when grown on sucrose.