Takehiro Unno

Cloning and heterologous expression of a glucodextranase gene from Arthrobacter globiformis I42, and experimental evidence for the catalytic diad of the recombinant enzyme

The gene encoding a glucodextranase from Arthrobacter globiformis I42 was cloned and, subsequently, heterologously expressed in Escherichia coli. This glucodextranase gene consists of 1048 amino acid residues with a calculated molecular mass of 109,135 Da. The roles of two residues at the active site of A. globiformis I42 glucodextranase were examined by site-directed mutagenesis. Glutamic acid residues 458 and 656, which are part of the apparent catalytic residues, were found to be essential for hydrolase activity.

A Glucodextranase Accompanied by Glucoamylase Activity from Arthrobacter globiformis I42

A glucodextranase was highly purified from a cell-free culture broth of Arthrobacter globiformis 142. The glucoamylase to glucodextranase activity ratio was almost the same (ca. 0.88 %) at each purification step. The activity profiles of the stabilities of the glucoamylase to pH and temperature coincided well with those of the glucodextranase. Furthermore, the inactivation profiles of the glucoamylase with various metal ions and inhibitors were almost the same as those of the glucodextranase. From these results, it was strongly suggested that a single enzyme molecule was responsible for both the glucodextranase and glucoamylase activities.