Characterization of a microsomal subfraction associated with mitochondria of the yeast, Saccharomyces cerevisiae. Involvement in synthesis and import of phospholipids into mitochondria

Abstract

In the yeast, Saccharomyces cerevisiae, similar to higher eukaryotes most phospholipids are synthesized in microsomes. Mitochondria contribute to the cellular biosynthesis of phospholipids insofar as they harbor phosphatidylethanolamine decarboxylase, and enzymes of phosphatidylglycerol and cardiolipin synthesis. In this paper we present evidence that certain enzymes of phospholipid biosynthesis, namely phosphatidylserine and phosphatidylinositol synthase, are enriched in a special microsomal fraction associated with mitochondria, which we named MAM. This fraction was isolated and characterized with respect to marker enzymes, protein and phospholipid composition, and enzymes of phospholipid synthesis. According to these analyses MAMs are a specialized subfraction of the endoplasmic reticulum, which is distinct from other microsomal subfractions. Phosphatidylserine synthesized in MAMs can be readily imported into mitochondria and converted to phosphatidylethanolamine. Reassociation of MAMs with purified mitochondria led to reconstitution of the import of phosphatidylserine into mitochondria. Organelle contact is suggested as a possible mechanism of this process.

One Single In-frame AUG Codon Is Responsible for a Diversity of Subcellular Localizations of Glutaredoxin 2 in Saccharomyces cerevisiae

“…In addition, we found a minor part of the immature form of Grx2 associated with membranes of the ER. Interestingly, a connection between mitochondrial and ER membrane systems has been postulated with the existence of the socalled "mitochondrial associated membrane fraction" (53). It remains to be clarified if the localization to ER membranes is a genuine property of Grx2 or due to an association with the mitochondrial associated membrane fraction.…”

Biochemistry, cell biology and molecular biology of lipids ofSaccharomyces cerevisiae

“…Most experimental evidence favours membrane contact as the mechanism of transport of PtdSer from MAM, a specialized subfraction of the endoplasmic reticulum, to mitochondria. 1,54,77 As was shown for mammalian MAM, 238 proteolytic treatment of yeast mitochondria negatively affected translocation of PtdSer. 275 Fusogenic proteins similar to those described for mammalian cells by Corazzi's group 33,211 and which are partially inactivated by exogenous proteases, may be involved in this process.…”

Import of sterols into mitochondria of the yeast Saccharomyces cerevisiae

“…Using mammalian cells, Ardail et al [13] demonstrated an interaction of contact sites with a specialized microsomal fraction, which catalyzes synthesis of phospholipids destined for the import into mitochondria. An analogous microsomal fraction, which had been originally described by Vance [14,15] for mammalian cells, was recently also characterized in yeast [16].…”