Lambda Receptor in the Outer Membrane of Escherichia coli as a Binding Protein for Maltodextrins and Starch Polysaccharides

Abstract

The starch polysaccharides amylose and amylopectin are not utilized by Escherichia coli , but are bound by the bacteria. The following evidence supports the view that the outer membrane λ receptor protein, a component of the maltose/ maltodextrin transport system is responsible for the binding. (i) Amylose and amylopectin both inhibit the transport of maltose into E. coli . (ii) Both polysaccharides prevent binding of non-utilizable maltodextrins by the intact bacterium, a process previously shown to be dependent on components of the maltose transport system (T. Ferenci, Eur. J. Biochem., in press). (iii) A fluorescent amylopectin derivative, O -(fluoresceinyl thiocarbamoyl)-amylopectin, has been synthesized and shown to bind to E. coli in a reversible, saturable manner. Binding of O -(fluoresceinyl thiocarbamoyl)-amylopectin is absent in mutants lacking the λ receptor, but mutations in any of the other components of the maltose transport system do not affect binding as long as λ receptor is present. (iv) Using the inhibition of λ receptor-dependent O -(fluoresceinyl thiocarbamoyl)-amylopectin binding as an assay, the affinities of the λ receptor for maltodextrins and other sugars have been estimated. The affinity for dextrins increases with increasing degree of polymerization ( K d for maltose, 14 mM; for maltotetraose, 0.3 mM; for maltodecaose, 0.075 mM). Maltose and some other di- and trisaccharides are inhibitory to amylopectin binding, but only at concentrations above 1 mM.