The herbicide phosphinothricin-tripeptide - a model for the analysis of the evolution of secondary metabolism in bacteria
WOLFGANG WOHLLEBEN
KLAUS SCHAD
EVA SCHINKO
Lehrstuhl für
Mikrobiologie/Biotechnologie
Universität Tübingen
Auf der Morgenstelle 28
D-72076 Tübingen
wowo@biotech.uni-tuebingen.de
http://www.mikrobio.uni-tuebingen.de/ag_wowo/index.php
Streptomyces
viridochromogenes produces the herbicide phosphinothricyl-alanyl-alanin
(phosphinothricin-tripeptide=PTT), which competitively inhibits bacterial
and plant glutamine synthetases. The biosynthesis starts with the synthesis
of the unusual amino acid N-acetyl-demethyl-phosphiniothricin (N-Ac-DMPT),
which is then linked to two alanine residues via non-ribosomal peptide
synthetases (NRPS). Within the PTT biosynthesis, two characteristics are
found which enable the analysis of the evolution of secondary metabolism
biosynthesis: three enzymes are involved in the biosynthesis of N-Ac-DMPT,
which are directly derived from enzymes of the TCC cycle; consequently,
S. viridochromogenes harbours the genes for the corresponding enzymes
of the primary metabolism as well as the genes for the secondary metabolism
enzymes. Especially the role of Pmi, a PTT-biosynthesis specific aconitase
which shows 64 % identity to the primary metabolism aconitase AcnA is
a central point of our studies. Despite their high sequence similarity,
both enzymes catalyze different reactions. Therefore, we are analysing
the changes in substrate specificity during evolution and the differentiation
dependent regulation of the enzymes.
In addition, the PTT biosynthesis represents the only known system, where
all peptide synthetase modules as well as the thioesterase-function are
located on separate proteins. In this case, the 'single enzyme system'
might be an archetype of the non-ribosomal peptide synthesis. Therefore,
we are studying the interaction of the single enzymes with the aim to
reproduce the evolution of this 'single enzyme system' to the multimodular
peptide synthetases and a first model of the assembly of the peptide synthetases
was developed.
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