Interaction of antibodies with liposomes bearing fluorescent haptens |
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Authors: | Ashot Petrossian John C Owicki |
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Institution: | Department of Biophysics and Medical Physics, University of California, Berkeley, and Division of Biology and Medicine, Lawrence Berkeley Laboratory, University of California, Berkeley, CA 94720 U.S.A. |
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Abstract: | Kinetic and equilibrium aspects of the recognition of antigenic model membranes by antibodies have been studied. Monoclonal anti-fluorescein IgG and its monovalent Fab fragment were allowed to interact with a fluorescein-lipid hapten that was incorporated into phospholipid vesicles. The binding was assayed in the nanomolar hapten concentration range by monitoring the quenching of hapten fluorescence by antibody. The rate and strength of the binding depended on the lipid composition of the vesicles; cholesterol enhanced both. The biphasic binding kinetics observed at high antibody concentrations for some compositions, plus additional spectroscopic evidence, led us to hypothesize that the hapten existed in a composition-dependent equilibrium between at least two conformations: (1) extended away from the membrane surface, available for binding, and (2) sequestered at or in the surface, unavailable for binding. The rate and strength of IgG binding were always greater than those of Fab, indicating bivalent binding by the IgG. This binding was intra-vesicular, since no agglutination of the vesicles was detected. |
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Keywords: | Membrane-antibody interaction Fluorescein-lipid hapten Liposome Lipid composition Kinetics Fluorescence Cbz carbobenzyloxyl 5-DCTAF 5-dichlorotriazinylaminofluorescein DEPC dielaidoylphosphatidylcholine DMPC dimyristoylphosphatidylcholine DOPC dioleoylphosphatidylcholine DPhPC diphytanoylphosphatidylcholine (di-3 7 11 15-tetramethylhexadecanoyl-PC) DPPC dipalmitoylphosphatidylcholine DPPE Dipalmityolphosphatidylethanolamine fluorescein-chlorotriazinyl-triglycyl-DPPE IgG immunoglobulin G NMR nuclear magnetic resonance PAGE polyacrylamide gel electrophoresis PC phosphatidylcholine PE phosphatidylethanolamine POPC l-palmitoyl-2-oleoylphosphatidylcholine SDS sodium dodecyl sulfate SIMS secondary-ion mass spectroscopy TLC thin-layer chromatography |
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