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J. Biochem, 2003, Vol. 134, No. 4 575-581
© 2003 Japanese Biochemical Society

BIOCHEMISTRY

More Ordered, Convex Ganglioside-Enriched Membrane Domains: The Effects of GM1 on Sphingomyelin Bilayers Containing a Low Level of Cholesterol

Bo Pei and Jian-Wen Chen*

National Laboratory of Biomacromolecules, Institute of Biophysics, Academia Sinica, Beijing 100101, China

The special physical state of the sphingolipid-enriched membranes with characteristic lipid composition, presently one of the most controversial foci in cell biology, provides the essential environment for the proteins inside to be involved in the related physiological processes. The role of gangliosides, an important component of the membranes, deserves attention. The present investigation using several biophysical techniques indicates that ganglioside GM1 induces the phase separation in the sphingomyelin membrane with 5 mol% cholesterol and regulates the membrane structure. The results of differential scanning calorimetry show that a higher Tm, GM1-rich phase emerges behind the lower Tm, sphingomyelin-rich phase with the incorporation of GM1 into the sphingomyelin/cholesterol bilayers; and the GM1-rich phase dominates the membrane when the proportion of GM1 reaches about 20 mol%. Fluorescence quenching further shows that the separation of the two domains is independent of temperature, occurring both in the gel phase and in the liquid phase. Laser Raman spectroscopy and fluorescence polarization suggest that the order of hydrocarbon chains increases and membrane fluidity decreases with increase in GM1 content. Use of the fluorescence probe merocyanine-540 and electron microscopy reveals that the insertion of GM1 leads to an increase in the spatial density of the lipid headgroups and a decrease in the curvature of the sphingomyelin/cholesterol bilayers. In sums, both the hydrophilic sugar heads and the hydrophobic hydrocarbon chains of GM1 contribute to the regulation of membrane architecture. We suggest that the convex curvature of ganglioside-enriched membrane could be involved in forming and maintaining the characteristic flask-shaped invagination of caveolae.

* To whom correspondence should be addressed. Tel: +86-10-64888523, Fax: +86-10-64872026, E-mail: chenmaci{at}sun5.ibp.ac.cn


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