Protein Complexome of Escherichia Coli Cell Envelope Under Proximately Physiological Conditions

The biological activity of a cell is performed by protein-protein interactions, and the interacted proteins are commonly assembled of a complex. Knowing a set of protein complexes of a cell, complexome, is essential for an understanding and global vision of cell functions. To visualize and identify membrane protein complexome of E. coli K-12 under close proximately physiological conditions on a proteome-wide scale, membrane protein fractions were analyzed by the combination of two dimensional native/SDS-PAGE (N-PAGE) with mass spectrometry in the present study. Sixteen distinct heteromeric protein complexes, interactions of membrane proteins with associated periplasmic and/or cytoplasmic proteins, were determined based on protein spots aligning in a vertical line and their functions correlation. Out of these sixteen complexes, eight were novel, in which four were first reported here and four had more components than before. The most interesting finding in the present study is that YaeT, the most crucial protein component of the known outer membrane assembly complex, interacted with the energy generation system Nar/Fdh-N. The finding may renew the knowledge that energy supply is not required for outer membrane assembly. Therefore, our results not only indicate that the N-PAGE with optimization is efficient and necessary approach to identify protein complexes, but also show that the interaction of membrane proteins with energy supply system is a characteristic feature in E. coli envelop.