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Journal of Bacteriology, September 2001, p. 5364-5370, Vol. 183, No. 18
Cambridge University Department of Pathology,
Cambridge, CB2 1QP, United Kingdom
Received 23 February 2001/Accepted 26 June 2001
The 1,024-amino-acid acylated hemolysin of Escherichia
coli subverts host cell functions and causes cell lysis. Both
activities require insertion of the toxin into target mammalian cell
membranes. To identify directly the principal toxin sequences dictating
membrane binding and insertion, we assayed the lipid bilayer
interaction of native protoxin, stably active toxin, and recombinant
peptides. Binding was assessed by flotation of protein-liposome
mixtures through density gradients, and insertion was assessed by
labeling with a photoactivatable probe incorporated into the target
lipid bilayer. Both the active acylated hemolysin and the inactive
unacylated protoxin were able to bind and also insert. Ca2+
binding, which is required for toxin activity, did not influence the in
vitro interaction with liposomes. Three overlapping large peptides were
expressed separately. A C-terminal peptide including residues 601 to 1024 did not interact in either assay. An internal peptide spanning
residues 496 to 831, including the two acylation sites, bound to
phospholipid vesicles and showed a low level of insertion-dependent
labeling. In vitro acylation had no effect on the bilayer interaction
of either this peptide or the full-length protoxin. An N-terminal
peptide comprising residues 1 to 520 also bound to phospholipid
vesicles and showed strong insertion-dependent labeling, ca. 5- to
25-fold that of the internal peptide. Generation of five smaller
peptides from the N-terminal region identified the principal
determinant of lipid insertion as the hydrophobic sequence
encompassing residues 177 to 411, which is conserved among
hemolysin-related toxins.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.18.5364-5370.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Membrane Interaction of Escherichia coli
Hemolysin: Flotation and Insertion-Dependent Labeling by
Phospholipid Vesicles
*
Corresponding author. Mailing address: Cambridge
University Department of Pathology, Tennis Court Rd.,
Cambridge, CB2 1QP, United Kingdom. Phone: 44-1223-333740. Fax:
44-1223-333327. E-mail: vk103{at}mole.bio.cam.ac.uk.
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