The hemolysin 11 from Bacillus cereus, HlyII, is a member of the beta-barrel pore-forming toxin family of secreted microbial proteins that includes the Staphylococcus aureus a-toxin. Compared with other proteins of the family, hemolysin 11 has 90 extra amino acids at its C-terminus. To examine more closely the cytotoxic and pore-forming properties of the protein, we have cloned and expressed it in Escherichia coli. We developed a purification procedure for the matured HlyII protein from both culture media and cell extracts using a combination of cation exchange and affinity chromatography together with gel-filtration. In both cases, the fully processed HlyII protein was purified as confirmed by N-terminal sequence analysis. The HlyII protein exhibits cytolytic activity of different extent on erythrocytes from various kinds of mammals. The results presented here show for the first time that two types of human cells are sensitive to HlyII action. In view of its broad cytotoxic activity as well as the ability to interact with artificial membranes, we assume that HlyII needs no specific receptor to bind to cell membranes. (c) 2005 Elsevier Inc. All rights reserved.