Carbohydrate-binding module of cycloisomaltooligosaccharide glucanotransferase from Thermoanaerobacter thermocopriae improves its cyclodextran production.

Thermoanaerobacter thermocopriae-derived thermostable cycloisomaltooligosaccharide (CI)-forming enzymes catalyze the production of CIs from dextran. The primary structure of the enzyme is comprised of CI glucanotransferase (TtCITase) at the N-terminal region and long isomaltooligosaccharide-forming enzyme (TtTGase) at the C-terminal region connected by carbohydrate-binding module family 35 (CBM, TtCBM). Three truncated mutants of CI-forming enzymes were successfully produced in Corynebacterium glutamicum, a food-grade host system, and their biochemical properties were characterized. The enzymes had optimum at pH 6.0 and pH-stability (5.0-12.0). Three enzymes had optimum temperature over 55 °C and they maintained 80% activity at 55 °C for 2 h, 12 h, and 18 h, respectively. Enzymes without CBM showed weaker allosteric behavior than those of other enzymes, which suggests the important role of CBM in allosteric behavior. However, CBM bearing enzymes showed high production of CIs with various degree of polymerization. These enzymes have potential application as the encapsulating material for insoluble pharmaceutical biomaterials.