pH-dependent Formation of Membranous Cytoplasmic Body-like
Structure of Ganglioside
GM1/Bis(Monoacylglycero)Phosphate Mixed Membranes
Tomohiro Hayakawa 1, Asami Makino 1, Motohide Murate 1, Ichiro Sugimoto 1, Yasuhiro Hashimoto 1, Hiroshi Takahashi 2, Kazuki Ito 1, Tetsuro Fujisawa 1, Hirotami Matsuo 3 and Toshihide Kobayashi 4*
1 RIKEN
2 Guma University
3 Shujitsu University
4 RIKEN Frontier Research System
* To whom correspondence should be addressed. E-mail: kobayasi{at}postman.riken.go.jp.
Submitted on October 2, 2006
Revised on October 10, 2006
Accepted on 11 October 2006
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Abstract |
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Membrane structures of the mixtures of ganglioside GM1 and endosome specific lipid, bis(monoacylglycero)phosphate (BMP, also known as lysobisphosphatidic acid, LBPA) were examined at various pH conditions by freeze-fracture electron microscopy and small-angle x-ray scattering (SAXS). At pH 8.5 - 6.5, a GM1/BMP (1/1 mol/mol) mixture formed small vesicular aggregates, whereas the mixture formed closely packed lamellar structures under acidic conditions (pH 5.5, 4.6) with the lamellar repeat distance of 8.06 nm. Since BMP alone exhibits a diffuse lamellar structure at a broad range of pH values and GM1 forms a micelle, the present results indicate that both GM1 and BMP are required to produce the closely stacked multilamellar vesicles. These vesicles resemble membranous cytoplasmic bodies (MCB) in cells derived from patients suffering from GM1 gangliosidosis. Similar to GM1 gangliosidosis, cholesterol was trapped in BMP vesicles in GM1- and in a low pH-dependent manner. Studies employing different gangliosides and a GM1 analog suggest the importance of sugar chains and a sialic acid of GM1 in the pH-dependent structural change of GM1/BMP membranes.
Key Words:
Lysobisphosphatidic acid, cholesterol, freeze fracture electron microscopy, gangliosidosis, late endosome, small-angle X-ray scattering
