Cr. Jones et al., High-affinity maltose binding and transport by the thermophilic anaerobe Thermoanaerobacter ethanolicus 39E, APPL ENVIR, 66(3), 2000, pp. 995-1000
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.