Membrane fusion correlates with surface charge in exocytic vesicles
1Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3200, USA.
Biochemistry
|June 16, 2004
Summary
Anionic lipids enhance gastric parietal cell tubulovesicular membrane fusion by increasing negative surface charge, lowering activation energy. This process is crucial for proton pump recruitment during acid secretion.
Area of Science:
- Cell Biology
- Membrane Biophysics
- Gastroenterology
Background:
- Gastric parietal cells secrete acid via proton pumps (H(+),K(+)-ATPase).
- Proton pumps are recruited to the apical membrane through tubulovesicular fusion.
- Previous studies reconstituted tubulovesicle fusion and showed lipid composition affects fusion.
Purpose of the Study:
- Investigate lipid requirements for tubulovesicular membrane fusion.
- Determine the role of membrane surface charge in fusion.
- Elucidate the mechanism by which lipids influence fusion.
Main Methods:
- Fluorescent probe relaxation assay.
- Protein transfer assays between tubulovesicles and liposomes.
- Fusion assays with synthetic liposomes and modified tubulovesicles.
- Varying lipid composition, charge, ionic strength, and temperature.
Main Results:
- Anionic lipids (phosphatidylserine, phosphatidic acid, phosphoinositides) significantly enhanced tubulovesicle-liposome fusion.
- Addition of anionic lipids increased tubulovesicle-tubulovesicle fusion in vitro.
- Fusion enhancement correlated with increased negative membrane surface charge.
- Increased ionic strength diminished the fusion-enhancing effect of anionic charges.
- Fusion was temperature-dependent, with anionic charges lowering activation energy.
Conclusions:
- Tubulovesicular fusion is enhanced by increased membrane surface negative charge.
- Anionic charges lower the activation energy for fusion.
- Neutralization or reversal of surface charge inhibits fusion.
- Membrane surface charge is a critical regulator of tubulovesicular fusion.
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