Graz University of Technology Austria Institute of Biochemistry ...

Cell Biology Group
Group leader: Günther Daum
Postdoctoral Fellow: Karlheinz Grillitsch (since May 2010)
PhD students: Melanie Connerth, Sona Rajakumari, Karlheinz Grillitsch (till March 2010),
Miroslava Spanova, Susanne Horvath, Martina Gsell, Vid V. Flis, Vasyl’ Ivashov, Lisa
Klug
Master students: Brigitte Wagner, Gerald Mascher
Technicians: Claudia Hrastnik, Alma Ljubijankic (since November 2010)
General description
Functional organelles are the basis for regulated processes within a cell. To sequester
organelles from their environment, membranes are required which not only protect the interior
of the organelles but also govern communication within the cell. To study biogenesis and
maintenance of biological membranes and assembly of lipids into organelle membranes our
laboratory makes use of the yeast as a well established experimental system. We combine
biochemical, molecular and cell biological methods addressing problems of lipid metabolism,
lipid depot formation and membrane biogenesis.
Specific aspects studied recently in our laboratory are (i) assembly and homeostasis of
phosphatidylethanolamine in yeast organelle membranes with emphasis on the role of the
major phosphatidylethanolamine synthesizing enzyme, the phosphatidylserine decarboxylase
1, (ii) neutral lipid storage in lipid particles/droplets and mobilization of these depots with
emphasis on the involvement of lipases and hydrolases, and (iii) characterization of organelle
membranes from the industrial yeast Pichia pastoris.
Phosphatidylethanolamine, a key component of yeast organelle membranes
Work from our laboratory and from other groups had shown that phosphatidylethanolamine
(PE), one of the major phospholipids of yeast membranes, is highly important for cellular
function and cell proliferation. PE synthesis in the yeast is accomplished by a network of
reactions including (i) synthesis of phosphatidylserine (PS) in the endoplasmic reticulum,
(ii) decarboxylation of PS by mitochondrial phosphatidylserine decarboxylase 1 (Psd1p) or
(iii) Psd2p in a Golgi/vacuolar compartment, (iv) the CDP-ethanolamine pathway (Kennedy
pathway) in the endoplasmic reticulum, and (v) the lysophospholipid acylation route catalyzed
by Ale1p and Tgl3p. To obtain more insight into biosynthesis, assembly and homeostasis of
PE, single and multiple mutants bearing defects in the respective pathways can be used.
Previous investigations in our laboratory were aimed at the molecular biological
identification of novel components involved in PE homeostasis of the yeast Saccharomyces
cerevisiae. For this purpose, a number of genetic screenings were performed. To obtain a
global view of the role of PE in the cell and to study the effects of an unbalanced PE level we
subjected a psd1∆ deletion mutant and the corresponding wild type to DNA microarray
analysis and examined genome-wide changes in gene expression. Comparison of the gene
expression pattern of the psd1∆ mutant with the wild type led to the identification of ~50
differentially expressed genes. Grouping of these genes into functional categories revealed
that PE formation by Psd1p influenced the expression of genes involved in diverse cellular
pathways including transport, carbohydrate metabolism and stress response. Currently, the
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