Molecular composition of the outer membrane of Escherichia coli and the importance of protein-lipopolysaccharide interactions.

Whole cells of Escherichia coli strains 0111, K12 and B as well as the ampicilln-resistant mutant K12 D21 and several lipopolysaccharide (LPS) mutants derived from this strain were analyzed for their molar LPS content per mg dry weight. An increase of the LPS concentration in some LPS mutants was substantiated by analyzing isolated cell walls and relating the molar LPS content to the murein subunit as measure of cell surface area. The increase of LPS was paralleled by increasing amounts of phospholipid while the overall protein content in the outer membrane decreased. According to the pattern of major outer membrane proteins in the various strains and the respective LPS structures, protein-LPS interactions are discussed as important requirements for outer membrane assembly and stability.