Isolation and Characterization of the Cellobiose Dehydrogenase from the Brown-Rot Fungus Coniophora puteana (Schum ex Fr.) Karst

The cellobiose dehydrogenase secreted by Coniophora puteana (Schum ex Fr) Karsten during growth on cellulose was isolated by successive anion-exchange chromatography on Q Sepharose fast flow and on TSK DEAE650S and gel filtration on Superose 12. The enzyme was recovered at a 41% yield with a 43-fold increase in specific activity. The purified sample was homogeneous by polyacrylamide gel electrophoresis (PAGE), sodium lauryl sulfate (SDS)-PAGE, and electrophoretic titration curve analysis and stained positively for glycoprotein (periodic acid/Schiff base reaction) and hemoprotein (peroxidase reaction). By isoelectric focusing over a narrow pH range two distinct bands were observed: a major band (pI 3.9) flanked by a minor band on its acidic side. FPLC gel filtration on TSK G3000 SW revealed a M, of 192,000, whereas on SDS-PAGE a single band, corresponding to a Mr of 111,000, was observed. The enzyme contained 13% sugar as mannose and upon digestion with endoglycosidase H, its molecular weight was lowered by 11 kDa. The enzyme showed a visible spectrum compatible with that of a b-type cytochrome containing a flavin cofactor. It was able to oxidize cellobiose, cellodextrins, and lactose at their C1-reducing group, with dichlorophenol indophenol as oxidant. Oxygen consumption (oxidase reaction in a Clark electrode) was not at a detectable rate. Km and Vmax for cellobiose oxidation were 84 μM and 2.98 μmol mg−1 min−1, respectively, hut the enzyme was strongly substrate (cellobiose)inhibited (Ksi 5.4 mM).