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Acknowledgments
We are grateful for financial support from National Nature Science Foundation of China (Project Nos. 30371727 and 30772766) and Nature Science Foundation of Jiangsu Province (Project Nos. BK2003113 and BK2007239). We also appreciate Prof. Neville Punchard for critical reading and kind help in editing of the manuscript.
Keywords
Outer-Membrane Factor proteins; TolC; AggA; Bacterial secretion; Type I secretion; Gram-negative bacteria; Electrophysiology
Introduction
Several different export pathways have evolved in microorganisms to facilitate the transport of a wide range of compounds from the M-344 to the extracellular medium. One wide-spread strategy in Gram-negative bacteria employs energized tripartite membrane pumps to export small noxious molecules and large proteins [1] and [2]. Once loaded with substrate, protein components at the inner-membrane recruit, with the help of a periplasmic adaptor complex, an outer-membrane channel–tunnel to form an active efflux pump spanning the entire bacterial cell envelope. Such a three-component assembly provides the structural means for the transport of protein substrates across the cell envelope of Gram-negative bacteria in one step, and defines type I secretion systems (TISS) [1].