The biosynthesis of natural products is characterized by its complex pathways and a high specificity of single reactions within these pathways leading to a specific product. Most of these reaction types and the corresponding catalyzing enzymes are attractive for an application in organic chemistry. One example is the oxidative coupling reaction which is characterized by its high reaction rates and efficiency under mild reaction conditions and plays a major role within the biosynthesis of lignans. Lignans are substantial components of plant cell walls. They are produced as a highly diverse group of plant defence compounds and due to their antimicrobial, antifeedant, antioxidant and antiviral features highly attractive for an application as pharmaceuticals. However, one of the most important reaction steps is the oxidative coupling of two monolignol units which are converted to free radicals by specific enzymes, like laccases or peroxidases preliminarily. The application of this phenoxy-radical coupling reaction in organic chemistry could open a synthetic access to pharmaceutically highly interesting compounds, but up to now its application is hindered by economic and ecological terms because of limited specificity and high amounts of side products. In nature, especially in biosynthesis of lignans, this problem is overcome with the help of dirigent proteins which allow a regio- and stereospecific control of oxidative coupling reactions and a unidirectional coupling of the free radicals leading to one specific product without side products.
The major challenge of this project was to open a broad access of these dirigent proteins to an application in organic chemistry and hence to overcome the ecological and economic issues of oxidative coupling reactions for an application as an efficient alternative to complex reaction sequences in chemical synthesis. To face this challenge, the participating research groups focussed on three major aspects: 1) Identification of suitable candidate genes for dirigent proteins in plant genomes. The best characterized DIRs are fiDir1 from Forsythia x intermedia and atDir6 isolated from Arabidopsis thaliana. During this project, more suitable candidate genes could be identified. Furthermore, the results of a multiple sequence analysis together with phylogenetic inference seem to confirm the hypothesis that one can attribute function (and even stereochemistry) based on sequence similarity. 2) The expression of known and newly identified genes of dirigent proteins in selected yeasts as expression hosts was quite challenging. Different yeast species, ranging from conventional baker’s yeast Saccharomyces cerevisiae over the methylotrophic yeast Hansenula polymorpha to other yeasts, like Kluyveromyces lactis and Yarrowia lipolyitca, were chosen due to the well-described ability to express proteins from other organisms and the difference in the modification of the produced proteins (glycosylation pattern). 3) Establishing a screening assay. Since dirigent proteins did not show own catalytic activity a suitable screening method was developed.
Participating Core Groups
Prof. Dr. Jörg Pietruszka, Dr. Martina Holz, Dr. Thomas Classen, Bioorganische Chemie, HHU Düsseldorf/FZ Jülich
Prof. Dr. Björn Usadel, Lehrstuhl für Botanik und Institut für Biologie I, RWTH Aachen
Dr. Thomas Classen
Bioorganische Chemie (BOC)
HHU Düsseldorf/FZ Jülich
Tel: +49 (0)2461 - 61-2208
DiPro is part of the NRW-Strategieprojekt BioSC and thus funded by the Ministry of Innovation, Science and Research of the German State of North Rhine-Westphalia.