Maltodextrin-binding proteins from diverse bacteria and archaea are potent solubility enhancers

In the biosynthesis of the C7-cyclitol moiety, valienol, of the -glucosidase inhibitor acarbose in Actinoplanes sp. SE50/110 various cyclitol phosphates, such as 1-epi-valienol-7-phosphate, are postulated precursors. In the cell extracts of Actinoplanes SE50/110 we found a new kinase activity which specifically phosphorylates 1-epi-valienol; other C7-cyclitol analogs were only weakly or not phosphorylated. The purified product of the kinase reaction turned out to be 1-epi-valienol-7-phosphate in analyses by nuclear magnetic resonance spectroscopy. The enzyme seems not to be encoded by an acb gene and, therefore, plays a role in a salvage pathway rather than directly in the de novo biosynthesis of acarbose.