Characterization of a thermostable cyclodextrin glucanotransferase from Pyrococcus furiosus DSM3638

A gene that encodes the enzyme Pyrococcus furiosus cyclodextrin glucanotransferase (PFCGT) was cloned in Escherichia coli. PFCGT was highly expressed in recombinant E. coli after compensation for codon usage bias using the pRARE plasmid. Purified PFCGT was extremely thermostable with an optimal temperature and pH of 95 degrees C and 5.0, respectively, retaining 97% of its activity at 100 degrees C. Incubation at 60 degrees C for 20 min during the purification process led to a 1.5-fold increase in enzymatic activity. A time course assay of the PFCGT reaction with starch indicated that cyclic alpha-1,4-glucans with DPs greater than 20 were produced at the beginning of the incubation followed by an increase in beta-CD. The major final product of PFCGT cyclization was beta-CD, and thus the enzyme is a beta-CGTase.