Although most glycosphingolipids (GSLs) are thought to be located in the outer leaflet of the plasma membrane, recent evidence indicates that GSLs and their precursor, ceramide, are also associated with intracellular organelles and, particularly, mitochondria. GSL biosynthesis starts with the formation of ceramide in the endoplasmic reticulum (ER), which is transported by controversial mechanisms to the Golgi apparatus, where stepwise addition of monosaccharides on to ceramides takes place. We now report the presence of GSL-biosynthetic enzymes in a subcompartment of the ER previously characterized and termed ‘mitochondria-associated membrane’ (MAM). MAM is a membrane bridge between the ER and mitochondria that is involved in the biosynthesis and trafficking of phospholipids between the two organelles. Using exogenous acceptors coated on silica gel, we demonstrate the presence of ceramide glucosyltransferase (Cer-Glc-T), glucosylceramide galactosyltransferase and sialyltransferase (SAT) activities in the MAM. Estimation of the marker-enzyme activities showed that glycosyltransferase activities could not be ascribed to cross-contamination of MAM by Golgi membranes. Cer-Glc-T was found to have a marked preference for ceramide bearing phytosphingosine as sphingoid base. SAT activities in MAM led to the synthesis of GM3 ganglioside and small amounts of GD3. GM1 was also synthesized along with GM3 upon incubation of the fraction with exogenous unlabelled GM3, underlying the presence of other sphingolipid-specific glycosyltransferases in MAM. On the basis of our results, we propose MAM as a privileged compartment in providing GSLs for mitochondria.
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Research Article|
May 01 2003
The mitochondria-associated endoplasmic-reticulum subcompartment (MAM fraction) of rat liver contains highly active sphingolipid-specific glycosyltransferases
Dominique ARDAIL;
Dominique ARDAIL
∗INSERM U 189, Department of Biochemistry, Lyon-Sud Medical School, B.P.12, 69921 Oullins Cedex, France
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Iuliana POPA;
Iuliana POPA
1
†INSERM U 346, Department of Dermatology, Edouard Herriot Hospital, 69437 Lyon Cédex 03, France
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Jacques BODENNEC;
Jacques BODENNEC
2
†INSERM U 346, Department of Dermatology, Edouard Herriot Hospital, 69437 Lyon Cédex 03, France
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Pierre LOUISOT;
Pierre LOUISOT
∗INSERM U 189, Department of Biochemistry, Lyon-Sud Medical School, B.P.12, 69921 Oullins Cedex, France
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Daniel SCHMITT;
Daniel SCHMITT
†INSERM U 346, Department of Dermatology, Edouard Herriot Hospital, 69437 Lyon Cédex 03, France
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Jacques PORTOUKALIAN
Jacques PORTOUKALIAN
3
†INSERM U 346, Department of Dermatology, Edouard Herriot Hospital, 69437 Lyon Cédex 03, France
3To whom correspondence should be addressed (e-mail [email protected]).
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Publisher: Portland Press Ltd
Received:
November 25 2002
Revision Received:
February 03 2003
Accepted:
February 11 2003
Accepted Manuscript online:
February 11 2003
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London ©2003
2003
Biochem J (2003) 371 (3): 1013–1019.
Article history
Received:
November 25 2002
Revision Received:
February 03 2003
Accepted:
February 11 2003
Accepted Manuscript online:
February 11 2003
Citation
Dominique ARDAIL, Iuliana POPA, Jacques BODENNEC, Pierre LOUISOT, Daniel SCHMITT, Jacques PORTOUKALIAN; The mitochondria-associated endoplasmic-reticulum subcompartment (MAM fraction) of rat liver contains highly active sphingolipid-specific glycosyltransferases. Biochem J 1 May 2003; 371 (3): 1013–1019. doi: https://doi.org/10.1042/bj20021834
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