Purification and characterization of the family J catalytic domain derived from the Clostridium thermocellum endoglucanase CelJ

The Clostridium thermocellum endoglucanase CelJ contains two different catalytic domains in a polypeptide, i,e., a subfamily E1 catalytic domain and a family J catalytic domain [J. Bacteriol., 178, 5732-5740 (1996)]. The family J catalytic domain (CDJ-CelJ) was produced by a recombinant Escherichia coli and purified, The purified CDJ-CelJ gave a single band on SDS-polyacrylamide gel electrophoresis and the molecular weight of this enzyme (60,000) was consistent with the value (60,333) calculated from the DNA sequence, CDJ-CelJ hydrolyzed various cellulosic substrates, xylan, and lichenan but not p-nitrophenyl (PNP)-cellobioside, PNP-glucoside, or PNP-xyloside at all, CDJ-CelJ was active on Avicel, a microcrystalline cellulose, and the specific activity of CDJ-CelJ on Avicel (0,0078U/mg protein) was comparable to that of CelS, which is recognized as the most important catalytic subunit of the C, thermocellum, cellulosome, suggesting that CelJ is also an important catalytic subunit in the cellulosome of this bacterium, in addition to CelS.