3‐Azi‐1‐methoxybutyl D‐maltooligosaccharides specifically bind to the maltose/maltooligosaccharide‐binding protein of Escherichia coli and can be used as photoaffinity labels

Abstract

Maltooligosaccharides with two to six (.alpha.1-4) linked glucose residues, carrying at their reducing end a 3-azi-1-methoxybutyl group in either .alpha. or in .beta. glycosidic linkage, were synthesized. These maltooligosaccharide analogues inhibit maltose uptake via the maltose-binding-protein-dependent transport system in Escherichia coli. The concentration of half-maximal inhibition of maltose transport, at 15 nM concentration, decreases with increasing chain length of the analogue, levelling off at 40 .mu.M after a chain length of four glucose residues in the .alpha. series and at 350 .mu.M after a chain length of three glucose residues in the .beta. series. The inhibition of maltose transport occurs at the level of the periplasmic maltose-binding protein. 3-Azi-1-methoxybutyl .alpha.-D-[3H]maltotrioside was bound by the maltose-binding protein with a Kd of 0.18 mM. Irradiation at 350 nm of purified maltose-binding protein in the presence of 4 .mu.M of this substrate labeled the protein covalently; labeling was prevented by 1 mM maltose. Using a crude preparation of periplasmic proteins two proteins were labeled, the maltose-binding protein and .alpha.-amylase. Thus, 3-azi-1-methoxybutyl .alpha.-D-maltooligosaccharides are potent photoaffinity labels for proteins with maltooligosaccharides-binding sites.