Self-Assembled Hybrid Nanoflowers of Manganese Phosphate and l-Arabinose Isomerase: A Stable and Recyclable Nanobiocatalyst for Equilibrium Level Conversion of d-Galactose to d-Tagatose

We report on the synthesis and characterization of a novel hybrid nanoflower of manganese and l-arabinose isomerase and its application in synthesis of d-tagatose, a rare sugar of high commercial value. An open reading frame of 1425 base pairs from Lactobacillus sakai was used to synthesis recombinant l-arabinose isomerase of 474 amino acids in E. coli. A hierarchical flower-like spherical structure with several nanopetals was self-assembled by using purified recombinant l-arabinose isomerase as the organic component and manganese phosphate as the inorganic component. The hybrid nanoflower was characterized by scanning electron microscopy, high-resolution transmission electron microscopy, confocal laser scanning microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Circular dichroism documented no change in structural properties of l-arabinose isomerase assembled in the hybrid nanoflower. Kinetic parameters of l-arabinose isomerase were improved in the hybrid nanoflower. l-Arabinose isomerase in the manganese hybrid nanoflower was found to convert d-galactose to d-tagatose with a conversion rate of ∼50%, without an addition of manganese in the reaction mixture. The hybrid nanoflowers exhibited excellent reusability and reproducibility during reaction cycle analysis. Hence, the developed manganese hybrid nanoflowers of l-arabinose isomerase shows promise for commercial production of the rare sugar d-tagatose.