A thermostable cellobiose phosphorylase from Thermoclostridium caenicola and its application to in vitro biotransformation

Cellobiose phosphorylase (CBP) catalyzes the reversible phosphorolysis of cellobiose to glucose and α-D-glucose-1-phosphate. CBPs play an important role in the in vivo enzymatic utilization of cellulosic materials. Here we discovered a novel CBP from Thermoclostridium caenicola (TcCBP), displaying 50-75 % sequence homology with previously reported CBPs. Recombinant TcCBP was well expressed in E. coli BL21(DE3), with a 1.6-fold increase in soluble expression levels over the widely-used Clostridium thermocellum CBP (CtCBP). This enzyme exhibited broad pH adaptability, maintaining substantial activities across pH 4.0-7.5 in the synthetic direction and pH 5.0-7.5 in the phosphorolytic direction. Compared to CtCBP, TcCBP displayed the superior thermostability and a nearly 100-fold improvement in "Product-to-Enzyme Ratio" (PE value). The biosynthesis of myo-inositol from cellobiose was conducted by using this CBP along with other four thermophilic enzymes (i.e., phosphoglucomutase, inositol 1-phosphate synthase, inositol monophosphatase, and polyphosphate glucokinase) in one pot without step-by-step addition of enzymes. Approximately 96 mM of myo-inositol was produced from 50 mM of cellobiose. These results indicated that this enzyme could be a potential thermophilic enzyme used for the production of value-added biochemicals by in vitro BioTransformation.