Localization of the dicarboxylate binding protein in the cell envelope of Escherichia coli K12

Abstract

Examination of the localization of the dicarboxylate binding protein (DBP) in the cell envelope of Escherichia coli K12 reveals that this protein is present on the cell surface, and also in the inner and outer regions of the periplasmic space. The cell surface DBP is released by treating the cells with EDTA. This protein can be surface labeled by lactoperoxidase radio-iodination, and by diazo[125I]iodosulfanilic acid in whole cells. It also binds tightly, but not covalently, to lipopolysaccharide. The DBP located in the outer region of the periplasmic space is released when the outer membrane is dissociated by EDTA – osmotic shock treatment. The DBP located in the inner region of the periplasmic space is released only when the EDTA – osmotic shocked cells are subjected to lysozyme treatment. At the moment, it is not certain whether this protein is bound to or trapped by the peptidoglycan network. This protein cannot be surface labeled in whole cells or in EDTA – osmotic shock treated cells; and it is not associated with lipopolysaccharide. Analysis of transport mutants indicates that these DBP are coded by the same gene.