Reconstitution of maltose transport in malB mutants of Escherichia coli through calcium-induced disruptions of the outer membrane

Abstract

The barrier function of the E. coli outer membrane against low concentrations of maltose in strains missing the λ receptor was partially overcome by treating the cells for 3 h with 25 mM Ca2+. Kinetic analysis of maltose transport revealed a Ca2+ - induced shift of the apparent Km of the system from about 100 μM in cells pretreated with Tris to about 15 μM in cells pretreated with Tris plus Ca2+. In contrast to maltose transport in untreated cells, that of Ca2+ - treated lamB cells was inhibited by molecules with a high molecular weight, such as amylopectin (molecular weight, 20,000), and anti-maltose-binding protein antibodies. In addition, lysozyme was shown to attack Ca2+-treated cells in contrast to untreated cells. The Ca2+ -induced permeability increase of the outer membrane allowed reconstitution of maltose transport in a mutant missing the maltose-binding protein with osmotic shock fluido containing the maltose-binding protein. Even though Ca2+-treatment allowed the entry of large molecules, the release of the periplasmic maltose-binding protein or alkaline phosphatase was negligible.