Arrangement of Proteins O-8 and O-9 in Outer Membrane of Escherichia coli K-12. Existence of Homotrimers and Heterotrimers

Abstract

The molecular arrangement of major outer membrane proteins O-8 and O-9 that exist as trimers was studied by cross-linking with dimethylsuberimidate. The cross-linked samples were examined on a urea/sodium dodecyl sulfate/polyacrylamide gel which was developed to separate cross-linked trimer and dimer of O-8 from those of O-9. Cells simultaneously synthesizing both O-8 and O-9 formed heterotrimers (trimers containing both proteins) as well as homotrimers. Quantitative analyses revealed that there was no discrimination between O-8 and O-9 in the assembly process to form trimers. When cells were grown sequentially under 2 different sets of conditions so that the cells synthesized either one of the 2 proteins in the 1st stage and the other in the 2nd stage of growth, no heterotrimers were formed. Subunit exchange did not take place between trimers which were incorporated into the outer membrane.