Paradoxical lipid dependence of pores formed by the Escherichia coli -Hemolysin in planar phospholipid bilayer membranes

¹ Instituto de Investigaciones Bioquímicas La Plata, INIBIOLP, Argentina
² Futron Corporation
³ National Institutes of Health

^* To whom correspondence should be addressed. E-mail: joshz{at}helix.nih.gov.

Submitted on May 25, 2006
Revised on June 13, 2006
Accepted on 26 June 2006

	Abstract

-Hemolysin is an extracellular protein toxin (117 KDa) secreted by Escherichia coli that targets the plasma membranes of eukaryotic cells. We studied the interaction of this toxin with membranes using planar phospholipid bilayers. For all lipid mixtures tested, addition of nanomolar concentrations of toxin resulted in an increase of membrane conductance and a decrease in membrane stability. HlyA decreased membrane lifetime up to three orders of magnitude in a voltage-dependent manner. Using a theory for lipidic pore formation, we analyzed this data in order to quantify how HlyA diminished the line tension of the membrane (i.e the energy required to form the edge of a new pore). However, in contrast to the expectation that adding the positive curvature agent lysophosphatidylcholine would synergistically lower line tension, its addition significantly stabilized HlyA-treated membranes. HlyA also appeared to thicken bilayers to which it was added. We discuss these results in terms of models for proteo-lipidic pores.

Key Words: BLM, Ion Channels, Proteo-lipidic pore, Toxin, curvature, lysolipids