Giant liposomes as model membranes for immunological studies: spontaneous insertion of purified K1-antigen (poly-alpha-2,8-NeuAc) of Escherichia coli.
A flow chamber has been constructed to use giant liposomes (diameter 5-50 microns) as model membranes for immunological studies and other experiments involving the interaction with water-soluble compounds. As an example of immunological importance, the insertion of purified K-antigen from Escherichia coli K1 has been studied. Despite its large hydrophilic part (poly-alpha-2,8-NeuAc), which is capped at its potential reducing end with phosphatidic acid acting as a lipid anchor group, this water-soluble material is readily incorporated into liposomal membranes of dimyristoylphosphatidylcholine (DMPC). The incorporation has been proven by immunofluorescence using a FITC-labeled monoclonal anti-K1-IgG. Without the lipid residue, however, no binding of poly-alpha-2,8-NeuAc to the liposomes has been observed. This could be shown by using colominic acid, an oligomeric form of alpha-2,8-NeuAc with free reducing ends instead of purified K1-antigen. The possibility for further manipulation of this model system has been shown by using a poly-alpha-2,8-NeuAc cleaving enzyme (endoneuraminidase). The function of the endoneuraminidase has been proven by showing no binding of the antibody after enzyme treatment of K1-bearing liposomes as well as by rapid loss of fluorescence of a previously bound FITC-antibody.
Johannes Gutenberg-Universität Mainz, Institut für Organische Chemie, F.R.G.
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G
Decher
H
H
Ringsdorf
J
J
Venzmer
D
D
Bitter-Suermann
C
C
Weisgerber
D000911:Antibodies, Monoclonal / Q000096:biosynthesis; D000942:Antigens, Bacterial / Q000276:immunology / Q000302:isolation & purification*; D000954:Antigens, Surface / Q000276:immunology / Q000302:isolation & purification*; D004134:Dimyristoylphosphatidylcholine; D004926:Escherichia coli / Q000032:analysis* / Q000276:immunology; D005455:Fluorescent Antibody Technique; D007074:Immunoglobulin G / Q000032:analysis; D008081:Liposomes / Q000276:immunology*; D008563:Membrane Lipids / Q000276:immunology; D008858:Microscopy, Phase-Contrast; D008954:Models, Biological; D009439:Neuraminidase / Q000302:isolation & purification; D012995:Solubility; D014867:Water
D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial; D000954:Antigens, Surface; D007074:Immunoglobulin G; C030659:K antigens; D008081:Liposomes; D008563:Membrane Lipids; D014867:Water; D009439:Neuraminidase; D004134:Dimyristoylphosphatidylcholine