Major Proteins of the Escherichia coli Outer Cell Envelope Membrane. Interaction of Protein II* with Lipopolysaccharide

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Abstract
One of the major proteins of the Escherichia coli outer cell envelope membrane, protein II*, is shown to interact specifically with the same membrane's lipolysaccharide. In cell envelopes the protein (Mr∼ 33 000) is partially degraded by trypsin or pronase, and fragments with molecular weights of 24 000 or 19 000, respectively, are left with the outer membrane. The protein and these fragments in the cell envelope can act as receptors for a phage, and, most likely, as receptors in F‐mediated conjugation. Lipopolysaccharide protects isolated protein II* (in solution) in the same way against proteolytic attack, and the tryptic or pronase fragments are identical with those fragments obtained from protease‐digested cell envelopes. All fragments represent the N‐terminal moiety of the protein, and are, in the presence of lipopolysaccharide, active as phage receptors. Protein II* is heat‐modifiable in that its apparent molecular weight upon boiling in dodecylsulfate is 33 000 and without boiling is 28 000. Addition of lipopolysaccharide to the boiled species causes a renaturation to the species of molecular weight 28 000. Total E. coli phospholipid, synthetic dimyristoyl phosphatidylcholine, or the oligosaccharide moiety of lipopolysaccharide do not show any of these effects. However, the lipid part of lipopolysaccharide (lipid A) exhibits essentially the same activity as complete lipopolysaccharide.All results taken together strongly suggest that the interaction observed in vitro reflects such an interaction in vivo, and the possibility exists that this interaction is at least partially responsible for the specific cellular localization of the protein. Very likely a number of other major outer membrane proteins also interact specifically with lipopolysaccharide.