Biochemical and genetic analyses of a novel γ-cyclodextrin glucanotransferase from an alkalophilic Bacillus clarkii 7364

Abstract

On screening for microorganisms in soil obtained in Japan that produce large amounts of γ-cyclodextrin (γ-CD), we identified a novel alkalophilic bacterium, Bacillus clarkii 7364. The cyclodextrin glucanotransferase (CGTase) secreted into the culture medium by this bacterium was purified by affinity chromatography on a γ-CD-immobilized column, followed by chromatography on a gel filtration column. The enzyme converted 13.7% of pre-gelatinized potato starch (10% w/w per reaction mixture) into CDs, and the majority (79%) of the product CDs was of the γ form. This property is quite unique among known CGTases and thus we named this enzyme γ-CGTase. The N-terminal and internal amino acid sequences of γ-CGTase were determined and used to design PCR primers for amplification of the nucleotide sequence that encodes the γ-CGTase gene. The entire gene sequence amplified by PCR was determined and then cloned into E. coli. The recombinant enzyme synthesized by E. coli retained biochemical properties quite similar to those of the original one. Comparison of the deduced amino acid sequence of γ-CGTase with those of other known CGTases that have different product specificities revealed the importance of subsites -3 and -7 for the preferential γ-cyclization activity.