E. coli hemolysin E (HlyE, ClyA, SheA): X-ray crystal structure of the toxin and observation of membrane pores by electron microscopy.

Hemolysin E (HlyE) is a novel pore-forming toxin of Escherichia coli, Salmonella typhi, and Shigella flexneri. Here we report the X-ray crystal structure of the water-soluble form of E. coli HlyE at 2.0 A resolution and the visualization of the lipid-associated form of the toxin in projection at low resolution by electron microscopy. The crystal structure reveals HlyE to be the first member of a new family of toxin structures, consisting of an elaborated helical bundle some 100 A long. The electron micrographs show how HlyE oligomerizes in the presence of lipid to form transmembrane pores. Taken together, the data from these two structural techniques allow us to propose a simple model for the structure of the pore and for membrane interaction.