Gene cloning, expression, and characterization of mutanase from Paenibacillus curdlanolyticus MP-1

Mutanases hydrolyze d-glucosidic linkages of α-1,3-linked polysaccharides which are important components of dental plaque. Therefore, these enzymes can be useful in preventive oral hygiene. A gene encoding mutanase was cloned from soil-isolated Paenibacillus curdlanolyticus MP-1 and expressed in Escherichia coli, and the resulting recombinant enzyme was characterized. The nucleotide sequence of the mutanase gene consisted of 3786 nucleotides encoding a protein of 1261 amino acids with a theoretical molecular weight of 131.62kDa. The deduced amino acid sequence exhibited a high degree of similarity with mutanases of Paenibacillus sp. KSM-M126 and Paenibacillus humicus NA1123, with 84% and 80% identity, respectively. The recombinant enzyme was purified 17.5-fold to homogeneity with a recovery of 37%. The purified mutanase showed optimal activity at pH 6.0 and 45°C, and was completely stable at pH 4.0-9.5 and up to 45°C. The enzyme was specific for α-1,3-glucosidic linkages and effectively solubilized fungal α-1,3-glucans and streptococcal mutans, releasing nigerooligosaccharides. The mutanase did not hydrolyze a synthetic substrate readily hydrolyzed by exoglucanases and the enzyme activity was not suppressed in the presence of deoxynojirimycin, an inhibitor of exo-type enzymes. These results suggest an endohydrolytic mode of action.