OUTER MEMBRANE VESICLE-MEDIATED EXPORT OF A PORE-FORMING CYTOTOXIN FROM ESCHERICHIA COLI

Abstract

ClyA, also called SheA or HlyE, is a four-helix bundle cytotoxic protein expressed by Escherichia coli and other enterobacteria. The expression of ClyA was shown to be controlled by the nucleoid protein H-NS and could be activated by overproduction of several different transcriptional regulators such as SlyA, MprA, HlyX, and FnrP. The ClyA protein contains two hydrophobic potential transmembrane domains. Lipid bilayer experiments and electron microscopic studies have led to the conclusion that ClyA forms stable pores in target membranes by assembling into ring-shaped toxin oligomers, but little or no effect was found on the bacterial cell membranes from which it is produced, presumably because the lytic activity of the protein is stimulated by cholesterol. Several studies have revealed that the ClyA toxin, which does not have any canonical signal sequence, nevertheless is secreted to the medium. It has become evident that a vesicle-mediated transport mechanism is responsible for the activation and delivery of ClyA protein, seemingly independent of the previously described type I–V secretion systems.

Keywords: :

• ClyA
• Pore-forming toxin
• Outer membrane vesicles
• Protein secretion.