High-affinity maltose binding and transport by the thermophilic anaerobe Thermoanaerobacter ethanolicus 39E

Thermoanaerobacter ethanolicus is a gram-positive thermophile that produces considerable amounts of ethanol from soluble sugars and polymeric substrat es, including starch. Growth on maltose, a product of starch hydrolysis, wa s associated with the production of a prominent membrane-associated protein that had an apparent molecular weight of 43,800 and was not detected in ce lls grown on xylose or glucose. Filter-binding assays revealed that cell me mbranes bound maltose with high affinity. Metabolic labeling of T, ethanoli cus maltose-grown cells with [C-14]palmitic acid showed that this protein w as posttranslationally acylated, A maltose-binding protein was purified by using an amylose resin affinity column, and the binding constant was 270 nM , Since maltase activity was found only in the cytosol of fractionated cell s and unlabeled glucose did not compete with radiolabeled maltose for uptak e in whole cells, it appeared that maltose was transported intact. In whole -cell transport assays, the affinity for maltose was approximately 40 nM, M altotriose and alpha-trehalose competitively inhibited maltose uptake in tr ansport assays, whereas glucose, cellobiose, and a range of disaccharides h ad little effect. Based on these results, it appears that T, ethanolicus po ssesses a high-affinity, ABC type transport system that is specific for mal tose, maltotriose, and alpha-trehalose.