Characterization of new membrane lipoproteins and their precursors of Escherichia coli

Abstract

By labeling cells heavily with [3H]glycerol or [3H]-palmitic acid several new species of lipoproteins, in addition to Braun's lipoprotein and a peptidoglycan-associated lipoprotein called PAL, were found in the envelope of Escherichia coli. The new lipoproteins were immunochemically different from both Braun's lipoprotein and PAL. A strain lacking the structural gene for Braun's lipoprotein contained new lipoproteins and PAL. In addition to Braun's lipoprotein and PAL, four new lipoproteins were found to be localized in the outer membrane, while other two species were found in the cytoplasmic membrane. The localization of one species is unknown. We previously reported that, on treatment of cells with globomycin, a precursor of Braun's lipoprotein accumulated in the cell envelope (Hussain, M., Ichihara, S., and Mizushima, S. (1980) J. Biol. Chem. 255, 3707-3712). Similarly, the putative precursors of new lipoproteins and that of PAL accumulated in globomycin-treated cells. These precursors contained glycerol and fatty acid(s) as that of Braun's lipoprotein did. It is suggested that the structures of the "signal" region and the mechanisms of processing of all the lipoproteins of E. coli are similar.