Staff Members of the Institute of Biochemistry, TU - Institut für ...

Molecular Biology Group
Karin Athenstaedt
Triacylglycerol synthesis in the oleaginous yeast Yarrowia lipolytica
The oleaginous yeast Yarrowia lipolytica has an outstanding capacity to accumulate huge
amounts of triacylglycerols (TAG). Along with other neutral lipids, TAG are stored in socalled
lipid particles. The structure of these cell compartments is rather simple. Mainly TAG
and steryl esters are forming a hydrophobic core which is surrounded by a phospholipid
monolayer with few proteins embedded. By growing Yarrowia lipolytica cells in media
containing, e.g., industrial fats or glycerol as a carbon source, the amount of TAG can be
increased up to 40% of cell dry weight. This ability leads to its application in biotechnological
processes such as single cell oil production or production of nutrients enriched in essential
fatty acids which can serve as nutritional complements. However, Yarrowia lipolytica may
also serve as a model organism to study lipid turnover in adipocytes, since not only the ability
to store excessive amounts of TAG in lipid particles but also the composition of this cell
compartment resembles adipocytes of higher eukaryotes. Despite these potentials of Yarrowia
lipolytica information about TAG (lipid) metabolism in this yeast is rather limited. Thus, we
started to investigate the proteome of Yarrowia lipolytica for proteins involved in TAG
synthesis. Homology searches with TAG synthases of other eukaryotes as queries highlighted
two candidate gene-products of the oleaginous yeast potentially catalyzing the formation of
TAG. A decreased amount of TAG in mutant cells defective in these candidate genes already
pinpointed to a function of these polypeptides in TAG formation. To investigate whether
these candidate genes encode true TAG synthases these genes were heterologously expressed
in cells of a Saccharomyces cerevisiae mutant defective in neutral lipid synthesis and as a
consequence lacking lipid particles (Fig. 1).
A B
C D
Figure 1: Restoration of lipid particle formation upon heterologous expression of Yarrowia
lipolytica TAG synthase candidates in mutant cells of the budding yeast Saccharomyces
cerevisiae lacking lipid particles.
In contrast to the negative control (B; mutant + empty plasmid), lipid particles are formed in
mutant cells transformed with plasmids bearing either of the respective candidate genes of
Yarrowia lipolytica (C, D). Panel A shows lipid particle formation in a wild-type cell of
Saccharomyces cerevisiae. Lipid particles are indicated by arrows. Size bar: 10 µm.
Fluorescent microscopic inspection and lipid analyses of the respective mutants clearly
demonstrated that these Yarrowia lipolytica genes encode true TAG synthases. The
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