Abstract
Translocation of presecretory proteins across the cytoplasmic membrane of Escherichia coli requires several Sec proteins and two kinds of energies, adenosine triphosphate (ATP) and a proton motive force. In vitro assay system established for the analysis of protein translocation revealed that ATP and the proton motive force play different roles in protein translocation. SecA, a peripheral membrane protein, was shown to be essential for in vitro protein translocation. SecE and SecY, both of which are integral membrane proteins, were purified from E. coli cells overproducing these proteins, and reconstituted into proteoliposomes. The reconstituted proteoliposomes exhibited protein translocation activity in the presence of ATP and SecA, indicating that SecE and SecY as well as SecA are indispensable components of protein translocation machinery. In this paper, the molecular mechanism of protein translocation across the membrane of E. coli is discussed based on the recent data obtained by both in vitro and reconstitution systems.
