Abstracts now available online - Euro Fed Lipid

Characterization of oxylipin producing enzymes
from Aspergillus nidulans
Ellen Hornung 1 , Nambirajan Govindarajan 1 , Nina Kassner 1 , Cornelia Göbel 1 , Silke
Busch 2 , Nancy P. Keller 3 , Gerhard H. Braus 2 and Ivo Feussner 1
1
Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University, D-37077
Göttingen, Germany
2
Institute for Microbiology and Genetics, Georg-August-University, D-37077 Göttingen,
Germany
3
Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI 53706,
USA
A sexual life cycle is unknown for most filamentous fungi of the Aspergillus group. A.
nidulans has been established as one of the major scientific model organisms for
filamentous fungi due to its ability to produce both asexual as well as sexual spores in
combination with an extensive secondary metabolism. It has been shown that the
formation of sexual fruitbodies containing the sexual ascospores is largely regulated by
oxylipins, which are oxygenated derivatives of different unsaturated fatty acids found in
the fungus. They function as so-called Psi factors (precocious sexual inducer). The
synthesis of these oxylipins is believed to be catalysed by the sequential action of at
least three groups of enzymes whereby the first reaction step is the best characterized
step till now. A first hydroxylation at position 8 adjacent to the ∆9-double bond of
unsaturated fatty acids is observed leading to formation of group of compounds named
psiB. It is catalyzed by a group of enzymes designated as “Ppo” enzymes (psi
producing oxygenase). The group contains three members namely Ppo A, B & C. The
second step is another hydroxylation at C-5 of the mono hydroxylated fatty acid leading
to 5,8-dihydroxy fatty acids, so-called psiC compounds. The last reaction step is a
lactonase reaction leading to cyclic modification of the carboxy group. These
substances are called psiA. Enzymes catalyzing the later two reaction steps have not
been identified till now. This study aims at investigating the formation of psiBs by PpoA
and PpoC. Thus the enzymes were heterologously expressed in the bakers yeast. The
enzymes were characterized by in vivo and in vitro studies using different fatty acids
substrates, namely linoleic, oleic, α-linolenic and palmitoleic acids. Products formed
were analyzed by HPLC/DAD and GC/MS.
P18