Graz University of Technology Austria Institute of Biochemistry ...

Molecular Biology Group
Group leader: Karin Athenstaedt
Postdoctoral Fellow: Andreas Beranek
Acyltransferases catalyzing 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, cell compartments with a rather simple structure. A neutral lipid core
mainly formed of TAG and steryl esters 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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