Escherichia coli alpha-hemolysin forms proteo-lipidic pores in membranes

V. HERLAX; L. BAKÁS

Angra dos Reis,Brasil

Congreso; I Latin American Protein Society Meeting; 2004

Latin American Protein Society (LAPS)

   Alpha-hemolysin is an extracellular protein toxin (107 KDa) secreted by Escherichia coli acts at level of the plasma membrane of target eukaryotic cells. We studied the interaction of this toxin with phospholipid membranes using artificial planar lipid membranes. For all lipid mixture tested, addition of nanomolar concentrations of toxin, resulted in an increase of bilayer conductance and a decrease in bilayer stability. Destabilization of the bilayer were quantified by using membrane lifetime measurements: HlyA decrease membrane lifetime up to three orders of magnitude in a voltage-dependent manner.   Non-lamellar lipid with positive intrinsic curvature lysophosphatidylcholine significantly reduce HlyA induced membrane destabilization. These results were in concordance with those obtained by leakage of fluorescent markers encapsulated in LUV composed of DOPC, compared with DOPC/LPC.In agreement with theory for lipidic pore formation, HlyA diminished the line tension of the membrane (i.e the energy required to formed the edge of a new pore). We suggest that this toxin protein acts by promoting the formation of proteo-lipidic pores al lytic concentration rather than forming purely proteinaceous ionic channels.