Institut für Pharmazeutische Biologie


 

 

The main focus of our research:

Most of our projects are aimed at the production of new therapeutic agents by „combinatorial biosynthesis”. Combinatorial biosynthesis is a procedure of molecular biology in which the combination of biosynthetical genes of different origins results in the formation of new natural products. We thereby concentrate on products with antibiotic activity isolated from actinomycetes which contain sugar moieties. Other projects deal with the investigation of the mechanisms leading to antibiotic activity of these oligosaccharides and the characterisation of the mechanisms leading to antibiotic resistance.

1. Production of new therapeutic agents by combinatorial biosynthesis

1. 1.
Cloning and identification of the antibiotic biosynthetic gene clusters
Antibiotic production genes commonly occur as a cluster in actinomycetes, i. e. they are situated closely together on a small part of the chromosome. This is referred to as a “biosynthetic gene cluster”. Our group has been able to clone the clusters of the antibiotics Phenalinolactone, Landomycin, Urdamycin, Granaticin, Avilamycin, Simocyclinon, Polyketomycin, Lipomycin and Aranciamycin. Most of the clusters have been fully sequenced.

1.1.1 Function determination of the clusters’ genes supposedly encoding glycosyltransferases
In all of the mentioned clusters, glycosyltransferase genes could be found encoding proteins which are in charge of attaching the sugars. We are currently investigating the specific function of these genes, mainly by means of gene inactivation and gene expression experiments. So far, the exact function could be assigned to several of these genes. Future work will include the isolation and characterisation of some of the glycosyltransferases.

1.1.2 Function determination of the clusters’ genes supposedly encoding enzymes which are involved in desoxygenation and methylation
Many antibiotics contain modified, i. e. desoxygenated and methlyated sugar derivatives which are important for their antibiotic activity. Several genes could be found in our clusters which are responsible for catalysing such modification reactions. Future work will focus on the characterisation of these genes by gene inactivation and gene expression experiments.

1.2 Application of biosynthetical genes for the production of novel bioactive agents
Some of the investigated genes are to be used for the targeted production of new antibiotics. Several experiments have shown that modified antibiotics can be designed by the heterologous expression of the respective biosynthetical genes. At present, our experiments concentrate mainly on glycosyltransferase genes.

1.3 Design of hybrid glycosyltransferases resulting in modified substrate specificity and application of the respective genes in combinatorial biosynthesis
We succeeded in producing “artificial” glycosyltransferase genes containing DNA elements of different genes. Their products showed enzymatical activity. We will continue to build new genes using gene shuffling and site directed mutagenesis methods which will result in customised enzymes with defined substrate specificity.

2.
Investigations on relations between structure and effect (Struktur-Wirkungsbeziehungen) of glycosylated natural products
Both the avilamycins and the landomycins exhibit strong antibiotic or cytotoxic activities. In both cases, the detailed mode of action is still unknown. Our work aims at constructing new derivatives in order to gain insight in the correlation between molecule structure and biological activity. The aim is to explore the detailed mode of action.

3.  
Investigations of mechanisms resulting in antibiotic resistance
We continue the work in identifying mechanisms of antibiotic resistance. We are highly interested in defining the genes conferring resistance to avilamycin. Two of the avilamycin resistance genes which have already been cloned take part in a novel resistance mechanism.