Serratia marcescens hemolysin (ShlA) binds artificial membranes and forms pores in a receptor-independent manner.

Both the inactive and active conformations of the hemolysin/cytolysin of Serratia marcescens (ShlA) binds membranes of erythrocytes, but only active ShlA is able to form pores. ShlA is unable to lyse prokaryotic membranes. To determine the receptors of the binding and pore-forming domains of active cytolysin on eukaryotic membranes, artificial large unilamellar vesicles (LUVs) of various membrane compositions were examined. In the current study, it is shown that significant pore formation and lysis was achieved with binary phosphatidylcholine/phosphatidylserine (PS) liposomes. No proteinaceous receptor was needed for either binding or pore formation by ShlA. Membrane integration and pore-forming activity were enhanced by addition of phosphatidylethanolamine. Phosphatidylserine is negatively charged at physiologic pH and is almost absent in prokaryotic membranes. Hence, membrane binding and insertion of ShlA are highly dependent on phosphatidylserine, which targets the toxic activity to eukaryotic cell membranes without any need of a proteinaceous receptor. This may explain why prokaryotic membranes were found to be resistant against ShlA in a previous study.