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J. Biol. Chem., Vol. 283, Issue 25, 17065-17074, June 20, 2008

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Structural and Biochemical Properties of Lipid Particles from the Yeast Saccharomyces cerevisiae^*

Tibor Czabany¹, Andrea Wagner¹, Dagmar Zweytick, Karl Lohner, Erich Leitner^¶, Elisabeth Ingolic^||, and Günther Daum²

From the Institute of Biochemistry, Graz University of Technology, Petersgasse 12, A-8010 Graz, Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, ^¶Institute for Food Chemistry and Technology, Graz University of Technology, Petersgasse 12, A-8010 Graz, and ^||Research Institute for Electron Microscopy and Finestructure Research, Graz University of Technology, Steyrergasse 17/III, A-8010 Graz, Austria

The two most prominent neutral lipids of the yeast Saccharomyces cerevisiae, triacylglycerols (TAG) and steryl esters (SE), are synthesized by the two TAG synthases Dga1p and Lro1p and the two SE synthases Are1p and Are2p. In this study, we made use of a set of triple mutants with only one of these acyltransferases active to elucidate the contribution of each single enzyme to lipid particle (LP)/droplet formation. Depending on the remaining acyltransferases, LP from triple mutants contained only TAG or SE, respectively, with specific patterns of fatty acids and sterols. Biophysical investigations, however, revealed that individual neutral lipids strongly affected the internal structure of LP. SE form several ordered shells below the surface phospholipid monolayer of LP, whereas TAG are more or less randomly packed in the center of the LP. We propose that this structural arrangement of neutral lipids in LP may be important for their physiological role especially with respect to mobilization of TAG and SE reserves.

Received for publication, January 16, 2008 , and in revised form, April 14, 2008.

^* This work was supported by the Fonds zur Förderung der Wissenschaftlichen Forschung inÖsterreich Projects 18857 and W901-B05 (to G. D.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Both authors contributed equally to this work.

² To whom correspondence should be addressed: Institute of Biochemistry, Graz University of Technology, Petersgasse 12/II, A-8010 Graz, Austria. Tel.: 43-316-873-6462; Fax: 43-316-873-6952; E-mail: guenther.daum{at}tugraz.at.

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