For secretion of proteins, E. coli possesses two distinct translocation systems, SecYEG and Tat. The vast majority of secretory proteins are translocated by the SecYEG system in an unfolded state, whereas the Tat system only accepts fully folded and often cofactorcontaining proteins for periplasmic export. The export of foreign proteins to the periplasm of E. coli is accomplished by harnessing endogenous protein translocation pathways, which is typically achieved by fusing a signal sequence to the target protein. The type of signal sequence used determines which export pathway is utilized by the target protein.
Citation: Bloois EV (2012) Biotechnological applications of periplasmic expression in E. coli. Enz Eng 1:e104.