Supermolecular structure of the enteropathogenic Escherichia coli type III secretion system and its direct interaction with the EspA-sheath-like structure

Abstract

Enteropathogenic Escherichia coli (EPEC) secretes several Esp proteins via the type III secretion system (secreton). EspA, EspB, and EspD are required for translocation of the effector proteins into host cells, in which EspB and EspD are thought to form a pore in the host membrane. Recent study has shown that EspA forms a filamentous structure that assembles as a physical bridge between bacteria and host cell surfaces, which then functions as a conduit for the translocation of bacterial effectors into host cells. To investigate the supermolecular structure of the type III secreton in EPEC, we partially purified it from the bacteria membrane and observed it via transmission electron microscopy. The EPEC type III secreton was composed of a basal body and a needle part and was similar to those of Salmonella and Shigella, except for a sheath-like structure at the tip of the needle. The length of sheath-like structures varied; it extended more than 600 nm and was 10 times longer than the Shigella needle part. The putative major needle component, EscF, was required for both secretion of Esp proteins and needle complex formation. Interestingly, elongation of the sheath-like structure was observed under constitutive expression of EspA but not of EscF. Furthermore, the transmission electron microscopy view with immunogold labeled anti-EspA antibodies clearly showed that EspA is a component of the sheath-like structure. This study revealed, to our knowledge for the first time, the supermolecular structure of the EPEC type III secreton and its direct association with the EspA-sheath-like structure.

A small-molecule inhibitor of the bacterial type III secretion system protects against in vivo infection with Citrobacter rodentium

“…Proteins were analyzed by immunoblotting with anti-EspB, 43 anti-EspF 42 and anti-GroEL (Sigma-Aldrich, St Louis, MO, USA) antibodies. For anti-Map antibodies, rabbits were immunized with Map-synthesized peptide (187-203 amino acids).…”

Enteropathogenic Escherichia coli , Shigella flexneri , and Listeria monocytogenes Recruit a Junctional Protein, Zonula Occludens-1, to Actin Tails and Pedestals

“…The EPEC-induced formation of pedestals is triggered by two bacterial factors, intimin and Tir (translocated intimin receptor) (28). Tir is one of the virulence factors termed "effectors," which are delivered directly into the host cytoplasm through bacterial secretion machinery termed the type III secretion system (TTSS) (24,46). The secreted Tir is in turn integrated into the plasma membrane and binds with a bacterial outer membrane protein, intimin (31).…”

Supramolecular Structure of the <i>Shigella</i> Type III Secretion Machinery

“…The basic morphological structure of the TTSM closely resembles that of the flagellar hook, basal body and C-ring (Fig. 4) (6,18,20,35,38).…”

“…The use of transmission electron microscopy (TEM) to visualize the TTSM was a landmark achievement in the field. Since then, the TTSM has been identified and visualized by TEM in many other pathogenic bacteria, including Shigella flexneri, Yersinia spp., and enteropathogenic Escherichia coli (EPEC) (6,17,18,35,38,46). Using the Shigella TTSS as an example, this review will present a brief overview of the TTSS while focusing on the mechanism of secretion and the assembly/architecture of the secretion system.…”