Enzymatic conversion of D-galactose to D-tagatose: Cloning, overexpression and characterization of L-arabinose isomerase from Pediococcus pentosaceus PC-5

The gene encoding L-arabinose isomerase from food-grade strain Pediococcus pentosaceus PC-5 was cloned and overexpressed in Escherichia coli. The recombinant protein was purified and characterized. It was optimally active at 50 degrees C and pH 6.0. Furthermore, this enzyme exhibited a weak requirement for metallic ions for its maximal activity evaluated at 0.6 mM Mn2+ or 0.8 mM Co2+. Interestingly, this enzyme was distinguished from other L-AIs, it could not use L-arabinose as its substrate. In addition, a three-dimensional structure of L.-AI was built by homology modeling and L-arabinose and D-galactose were docked into the active site pocket of PPAI model to explain the interaction between L-AI and its substrate. The purified P. pentosaceus PC-5 L-AI converted P-galactose into D-tagatose with a high conversion rate of 52% after 24 h at 50 degrees C, suggesting its excellent potential in D-tagatose production. Crown Copyright (C) 2013 Published by Elsevier GmbH. All rights reserved.