title: Acidic pH-induced membrane insertion of colicin A into E. coli natural lipids probed by site-directed spin labeling.
abstract: Colicin A is a pore-forming toxin that forms a voltage-gated channel in the inner membrane of the target bacteria. The structures of the closed and open channel states of membrane-bound colicin A are not resolved. In the present site-directed spin-labeling study, the insertion-competent state of colicin A is provoked by an acidic pH jump prior to the insertion into liposomes prepared from Escherichia coli natural lipids. The membrane-bound colicin A is able to open a voltage-dependent channel as demonstrated by the efflux of tempophosphate spin label from the lumen of liposomes. The EPR spectra of spin-labeled colicin A variants in the membrane-bound closed channel state reveal a conformational equilibrium with resolved interhelical tertiary contacts. The spin label accessibility and polarity profiles suggest the amphipathic helices (H1-H7 and H10) to be located in the membrane close to the membrane-water interface and the hydrophobic hairpin (H8 and H9) to be immersed more deeply in the membrane.
authors: University of Osnabrück, Barbarastrasse 7, D-49069 Osnabrück, Germany.
authors: Lakshmi Padmavathi
authors: LP
authors: Pulagam
authors: Heinz-Jürgen
authors: HJ
authors: Steinhoff
mesh_terms: D002462:Cell Membrane / Q000737:chemistry / Q000235:genetics; D003087:Colicins / Q000737:chemistry* / Q000235:genetics*; D004578:Electron Spin Resonance Spectroscopy; D048168:Escherichia coli K12 / Q000737:chemistry* / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D008563:Membrane Lipids / Q000737:chemistry* / Q000235:genetics*; D008958:Models, Molecular; D016254:Mutagenesis, Insertional; D011485:Protein Binding / Q000235:genetics; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D013113:Spin Labels; D019097:Spin Trapping
chemical_list: D003087:Colicins; D029968:Escherichia coli Proteins; D008563:Membrane Lipids; D013113:Spin Labels