Recombinant membrane proteins in Escherichia coli are either expressed at relatively low level in the cytoplasmic membrane or they accumulate as inclusion bodies. Here, we report that the abundant over-production of subunit b of E. coli F1Fo ATP synthase in the mutant host strains E. coli C41(DE3) and C43(DE3) is accompanied by the proliferation of intracellular membranes without formation of inclusion bodies. Maximal levels of proliferation of intracellular membranes were observed in C43(DE3) cells over-producing subunit b. The new proliferated membranes contained all the over-expressed protein and could be recovered by a single centrifugation step. Recombinant subunit b represented up to 80% of the protein content of the membranes. The lipid:protein ratios and phospholipid compositions of the intracellular membranes differ from those of bacterial cytoplasmic membranes, and they are particularly rich in cardiolipin.
