The major proteins of the Excherichia coli outer cell envelope membrane. Preparative isolation of all major membrane proteins

Abstract

A procedure is described that from one batch of cells allows the isolation of all major proteins of the outer cell envelope membrane of Escherichia coli B/r. The method involves differential extraction of cell envelopes with ionic and non-ionic detergents with and without Mg2+ present, and the proteins are finally separated by molecular sieve chromatography in the presence of sodium dodecylsulfate. From 200 g cell paste in ten days (including the five days chromatography) approximately 120 mg protein I (molecular weight approximately 38,000), approximately 110 mg protein II* (molecular weight approximately 33,000), approximately 50 mg protein III (molecular weight approximately 17,000), and approximately 30 mg protein IV (molecular weight approximately 7,000) are obtained in pure state, and these yields are near the expected ones assuming quantitatve recoveries. Protein II* is a heat-modifiable protein (perhaps due to complete unfolding and/or binding of sodium dodecyl-sulfate only at higher temperatures), and the isolated protein is completely in its unmodified form. Protein IV, Braun's lipoprotein, in the cell envelope exists in two forms, one covalently bound to the murein layer and the other not. The isolated protein IV represents the free form of the protein that so far had not been isolated; its protein part dies not differ substantially from that of the bound form.