Gene cloning, functional expression and characterisation of a novel glycogen branching enzyme from Rhizomucor miehei and its application in wheat breadmaking.

A gene (RmGBE) encoding a glycogen branching enzyme from Rhizomucor miehei was cloned into the pET28a (+) vector and expressed in Escherichia coli, and biochemically analysed. RmGBE had an open reading frame of 2097bp encoding 698 amino acid residues. The purified enzyme was a monomer of 78.1kDa. RmGBE was optimally active at 25°C and pH 7.5. It displayed excellent cold adaptation over a low temperature range of 10-30°C, retaining over 85% of its relative activity. RmGBE showed the highest specificity to amylose, about ten times higher than to amylopectin. Addition of RmGBE to wheat bread resulted in a 26% increase in specific volume and a 38% decrease in crumb firmness in comparison with the control. Besides, the retrogradation of bread was significantly retarded along with the enzyme reaction. These properties make RmGBE highly useful in the food and starch industries.