Characterization of maltose and maltotriose transport in the acarbose-producing bacterium Actinoplanes sp.

Acarbose, a pseudomaltotetraose, is produced by strains of the genus Actinoplanes. The compound is an inhibitor of alpha-glucosidases and is used in the treatment of patients suffering from type II diabetes. The benefits of acarbose for the producer are not known; however, a role as carbophor has been proposed. Acarbose synthesis is induced in the presence of maltose and maltotriose. We have investigated the transport activities for these sugars in Actinoplanes sp. strain SN 223/29 grown on different carbon sources, including acarbose. Under the conditions used, Actinoplanes sp. utilized acarbose as sole source of carbon and energy, although growth ceased after 24 h, possibly due to the accumulation of a toxic degradation product in the cytosol. Maltose transport was observed in cells grown on each of the substrates tested except glucose. Maltose transport of acarbose-grown cells was inhibited by sucrose and trehalose and, to a lesser extent, by maltodextrins but not by acarbose. In contrast, in maltose/maltotriose-grown cells maltose uptake was inhibited by acarbose. Maltotriose uptake in these cells was less inhibited by maltose but was more sensitive to acarbose than in acarbose-grown cells. The Km and Vmax values of maltose uptake are in the range of those reported for binding protein-dependent sugar ATP-binding cassette (ABC) transport systems. A maltose-binding protein that does not bind acarbose was isolated from cells grown on either acarbose, glycerol or maltose. These results suggest that an acarbose-insensitive maltose/sucrose/trehalose transporter that also accepts maltodextrins operates in acarbose-grown cells while a maltodextrin transporter that accepts maltose/sucrose/trehalose and is moderately sensitive to acarbose is found in cells grown in maltose/maltotriose-containing media.