Specific phosphatidylethanolamine dependence of Serratia marcescens cytotoxin activity
Abstract
The cytolytic and haemolytic activity of Serratia marcescens is determined by the ShlA protein, which is secreted across the outer membrane with the aid of the ShlB protein. In the absence of ShlB, inactive ShlA* remains in the periplasm of Escherichia col transformed with an shlA-encoding plasmid, which indicates that ShlB converts ShlA* to active ShlA. ShlA* in a periplasmic extract and partially purified ShlA* were activated in vitro by partially purified ShlB. When both proteins were highly purified, ShlA* was only activated by ShlB when phosphatidylethanolamine (PE) or phosphatidylserine was added to the assay, while phosphatidylglycerol contributed little to ShlA* activation. Lyso-PE, cardiolipin, phosphatidylcholine, phosphatidic acid, lipopolysaccharide and various detergents could not substitute for PE. Although radioactively labelled PE was so tightly associated with ShlA that it remained bound to ShlA after heating and SDS-PAGE, it was not covalently linked to ShlA as PE could be removed by thin-layer chromatography with organic solvents. The number of PE molecules associated per molecule of ShlA was 3.9 +/- 2.2. Active ShlA was inactivated by treatment with phospholipase A2, which indicated that PE is also required ...Continue Reading
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