The filamentous type III secretion translocon of enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) uses a type III secretion system ( TTSS) to inject effector proteins into the plasma membrane and cytosol of i nfected cells. To translocate proteins, EPEC, like Salmonella and Shigella, is believed to assemble a macromolecular complex (type III secreton) that spans both bacterial membranes and has a short needle-like projection. Howe ver, there is a special interest in studying the EPEC TTSS owing to the fac t that one of the secreted proteins, EspA, is assembled into a unique filam entous structure also required for protein translocation. In this report we present electron micrographs of EspA filaments which reveal a regular segm ented substructure. Recently we have shown that deletion of the putative st ructural needle protein, EscF, abolished protein secretion and formation of EspA filaments. Moreover, we demonstrated that EspA can bind directly to E scF, suggesting that EspA filaments are physically linked to the EPEC needl e complex. In this paper we provide direct evidence for the association bet ween an EPEC bacterial membrane needle complex and EspA filaments, defining a new class of filamentous TTSS.