Cholesterol in Negatively Charged Lipid Bilayers Modulates the Effect of the Antimicrobial Protein Granulysin |
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Authors: | Hanna Barman Michael Walch Sonja Latinovic-Golic Claudia Dumrese Max Dolder Peter Groscurth Urs Ziegler |
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Institution: | (1) Division of Cell Biology, Institute of Anatomy, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland;(2) Present address: Institute of Medical Microbiology, University of Zurich, Gloriastrasse 32, CH-8006 Zurich, Switzerland |
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Abstract: | The release of granulysin, a 9-kDa cationic protein, from lysosomal granules of cytotoxic T lymphocytes and natural killer
cells plays an important role in host defense against microbial pathogens. Granulysin is endocytosed by the infected target
cell via lipid rafts and kills subsequently intracellular bacteria. The mechanism by which granulysin binds to eukaryotic
and prokaryotic cells but lyses only the latter is not well understood. We have studied the effect of granulysin on large
unilamellar vesicles (LUVs) and supported bilayers with prokaryotic and eukaryotic lipid mixtures or model membranes with
various lipid compositions and charges. Binding of granulysin to bilayers with negative charges, as typically found in bacteria
and lipid rafts of eukaryotic cells, was shown by immunoblotting. Fluorescence release assays using LUV revealed an increase
in permeability of prokaryotic, negatively charged and lipid raft-like bilayers devoid of cholesterol. Changes in permeability
of these bilayers could be correlated to defects of various sizes penetrating supported bilayers as shown by atomic force
microscopy. Based on these results, we conclude that granulysin causes defects in negatively charged cholesterol-free membranes,
a membrane composition typically found in bacteria. In contrast, granulysin is able to bind to lipid rafts in eukaryotic cell
membranes, where it is taken up by the endocytotic pathway, leaving the cell intact. |
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Keywords: | Cholesterol Lipid bilayer Granulysin AFM Cytotoxicity Lipid rafts |
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