Complexome of Escherichia coli envelope proteins under normal physiological conditions.

The interactions between proteins are important for very numerous, if not all, biological functions, and the interacted proteins might form part of a protein complex. To understand the protein complexes of a cell, complexome, is essential for a better understanding of cell functions. In the present study, we have performed a systematic fractionation and analysis of Escherichia coli K-12 membrane proteins under proximately normal physiological conditions using two-dimensional native/SDS-PAGE (N-PAGE)-based proteomics. Sixteen distinct heteromeric protein complexes including their associated periplasmic and/or cytoplasmic proteins were determined based on the distribution patterns of the protein spots in the gel and proteins' functions. Out of these 16 complexes, 10 were novel ones, in which six were reported here for the first time and the other four contained novel components that have not been reported previously. Interestingly, YaeT, one of the most important protein components in the well-known outer membrane assembly complex, was found to interact with the energy generation system Nar/Fdh-N. This finding may modify the previously well-accepted concept that energy supply is not required for outer membrane assembly, and suggest that the interaction of membrane proteins with energy supply system is a characteristic feature of E. coli envelope protein network.