Distribution of ganglioside GM1 in L-alpha-dipalmitoylphosphatidylcholine/cholesterol monolayers: a model for lipid rafts.
The distribution of low concentrations of ganglioside GM1 in L-alpha-dipalmitoylphosphatidylcholine (DPPC) and DPPC/cholesterol monolayers supported on mica has been studied using atomic force microscopy (AFM). The monolayers studied correspond to a pure gel phase and a mixture of liquid-expanded (LE) and liquid-condensed (LC) phases for DPPC and to a single homogeneous liquid-ordered phase for 2:1 DPPC/cholesterol. The addition of 2.5-5% GM1 to phase-separated DPPC monolayers resulted in small round ganglioside-rich microdomains in the center and at the edges of the LC domains. Higher amounts of GM1 (10%) give numerous filaments in the center of the LC domains and larger patches at the edges. A gel phase DPPC monolayer containing GM1 showed large domains containing a network of GM1-rich filaments. The addition of GM1 to a liquid-ordered 2:1 DPPC/cholesterol monolayer gives small, round domains that vary in size from 50 to 150 nm for a range of surface pressures. Larger amounts of GM1 lead to coalescence of the small, round domains to give longer filaments that cover 30-40% of the monolayer surface for 10 mol % GM1. The results indicate that biologically relevant GM1 concentrations lead to submicron-sized domains in a cholesterol-rich liquid-ordered phase that is analogous to that found in detergent-insoluble membrane fractions, and are thought to be important in membrane microdomains or rafts. This demonstrates that AFM studies of model monolayers and bilayers provide a powerful method for the direct detection of microdomains that are too small for study with most other techniques.
Yuan
C
C
Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada.
Johnston
L J
LJ
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002417:Cattle; D002784:Cholesterol / Q000737:chemistry*; D005677:G(M1) Ganglioside / Q000737:chemistry*; D066298:In Vitro Techniques; D008563:Membrane Lipids / Q000737:chemistry; D018625:Microscopy, Atomic Force; D008956:Models, Chemical
D008563:Membrane Lipids; D015060:1,2-Dipalmitoylphosphatidylcholine; D005677:G(M1) Ganglioside; D002784:Cholesterol