pH dependence of listeriolysin O aggregation and pore-forming ability.
Listeriolysin O (LLO) is the major factor implicated in the escape of Listeria monocytogenes from the phagolysosome. It is the only representative of cholesterol-dependent cytolysins that exhibits pH-dependent activity. Despite intense studies of LLO pH-dependence, this feature of the toxin still remains incompletely explained. Here we used fluorescence and CD spectroscopy to show that the structure of LLO is not detectably affected by pH at room temperature. We observed slightly altered haemolytic and permeabilizing activities at different pH values, which we relate to reduced binding of LLO to the lipid membranes. However, alkaline pH and elevated temperatures caused rapid denaturation of LLO. Aggregates of the toxin were able to bind Congo red and Thioflavin T dyes and were visible under transmission electron microscopy as large, amorphous, micrometer-sized assemblies. The aggregates had the biophysical properties of amyloid. Analytical ultracentrifugation indicated dimerization of the protein in acidic conditions, which protects the protein against premature denaturation in the phagolysosome, where toxin activity takes place. We therefore suggest that LLO spontaneously aggregates at the neutral pH found in the host cell cytosol and that this is a major mechanism of LLO inactivation.
Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia.
Andrej
A
Bavdek
Rok
R
Kostanjšek
Valeria
V
Antonini
Jeremy H
JH
Lakey
Mauro
M
Dalla Serra
Robert J C
RJ
Gilbert
Gregor
G
Anderluh
D001427:Bacterial Toxins / Q000737:chemistry* / Q000378:metabolism*; D002942:Circular Dichroism; D003001:Cloning, Molecular; D003603:Cytotoxins / Q000737:chemistry* / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005453:Fluorescence; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000378:metabolism*; D006460:Hemolysin Proteins / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D052899:Pore Forming Cytotoxic Proteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D011994:Recombinant Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D020349:Surface Plasmon Resonance
D001427:Bacterial Toxins; D003603:Cytotoxins; D006360:Heat-Shock Proteins; D006460:Hemolysin Proteins; D008051:Lipid Bilayers; D052899:Pore Forming Cytotoxic Proteins; D011994:Recombinant Proteins; C038705:hlyA protein, Listeria monocytogenes