Segregation of Gangliosides GM1 and GD3 on Cell Membranes, Isolated Membrane Rafts, and Defined Supported Lipid Monolayers

Kavita A. Vyas, Himatkumar V. Patel, Alka A. Vyas and Ronald L. Schnaar

Abstract

Lateral assemblies of sphingolipids, glycosphingolipids and cholesterol, termed rafts, are postulated to be present in biological membranes and to function in important cellular phenomena. We probed whether rafts are heterogeneous by determining the relative distribution of two gangliosides, GM1 and GD3, in artificial supported monolayers, in intact rat primary cerebellar granule neurones, and in membrane rafts isolated from rat cerebellum. Fluorescence resonance energy transfer (FRET) using fluorophore labelled cholera toxin B subunit (which binds GM1) and mAb R24 (which binds GD3) revealed that GM1 spontaneously selfassociates but does not cocluster with GD3 in supported monolayers and on intact neurones. Cholera toxin and immunocytochemical labelling of isolated membrane rafts from rat cerebellum further demonstrated that GM1 does not colocalise with GD3. Furthermore, whereas the membrane raft resident proteins Lyn and caveolin both colocalise with GD3 in isolated membrane rafts, GM1 appears in separate and distinct aggregates. These data support prior reports that membrane rafts are heterogeneous, although the mechanisms for establishing and maintaining such heterogeneity remain to be determined.

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Biological Chemistry keeps you up-to-date with the latest advances in the molecular life sciences. The journal publishes Research Articles, Short Communications, Reviews and Minireviews. Areas include: general biochemistry/pathobiochemistry, structural biology, molecular and cellular biology, genetics and epigenetics, virology, molecular medicine, plant molecular biology/biochemistry and novel experimental methodologies.

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