Acyl chains are responsible for the irreversibility in the Escherichia coli alpha-hemolysin binding to membranes.

Hemolysin (HlyA) is an extracellular protein secreted by uropathogenic strains of Escherichia coli. The mature HlyA is able to bind to mammalian target cell membranes including those of the immune system, causing lysis. The lytic activity is absolutely dependent upon the Hlyc-dependent acylation of Prohemolysin. In this paper we show, through Trp fluorescence studies and denaturation in Guanidine hydrochloride, that the acylation is responsible for the loose conformation of the active protein, necessary to transform it from soluble to membrane-bound form. Previous studies showed that toxin binding to the bilayers occurs in, at least two ways, a reversible adsorption and irreversible insertion. We demonstrated that the irreversibility is due to the acyl chains in the HlyA, as shown by the protein transfer from multilamellar liposomes composed of palmitoyl-oleoyl-phosphatidylcholine (POPC) to large unilamellar vesicles containing POPC-doxyl as protein fluorescence quencher.