Electrostatic interactions of colicin E1 with the surface of Escherichia coli total lipid

The surface properties of colicin El, a 522-amino acid protein, and its interaction with monolayers of Escherichia coli (E. coli) total lipid and 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DOPC) were studied using the Langmuir-Blodgett (LB) technique. Colicin El is amphiphilic, forming a protein monolayer at the air/buffer interface. The protein is thought to interact with the E. coli total lipid head groups through electrostatic interactions, followed by its insertion into the lipid monolayers. Supported lipid bilayers (SLBs) of E. coli total lipid and DOPC, deposited onto mica at the cell membrane equivalence pressure for E. coli and incubated with colicin El, were imaged by contact mode atomic force microscopy (CM-AFM). Colicin El formed protein aggregates on DOPC SLBs, while E. coli total lipid SLB was deformed following its incubation with colicin El. Corresponding lateral force images, along with electrostatic surface potentials for colicin E1 P190, imply a direct interaction of colicin El with lipid head groups facilitating their charge neutralization. (c) 2006 Elsevier B.V. All rights reserved.