Forschungsaktivitäten
Erforschung der mikrobiellen Virulenz auf molekularer Ebene
Ein Schwerpunkt unserer Forschung besteht darin, herauszufinden, wie pathogene Bakterien bei einer Infektion mit den Komponenten der Wirtszelle interagieren. Zurzeit befassen wir uns mit den Proteinen, die die Virulenz von Listeria monocytogenes (Zusammenarbeit mit Jürgen Wehland, HZI und Pascale Cossart, Paris), enteropathogenen E. coli (EPEC) (Zusammenarbeit mit Theresia Stradal und Klemens Rottner, HZI) und Yersinia enterocolitica (Zusammenarbeit mit Guy Cornelis, Basel und Petra Dersch, Braunschweig) bestimmen, sowie mit den entsprechenden Interaktionspartnern (Rezeptoren) der Wirtszelle.
Invasion by Listeria monocytogenes
The facultative intracellular human pathogen L. monocytogenes produces a distinct number of virulence factors, that usually mimic host cell processes leading e.g. to invasion and propagation within the host. In the past we have determined the high resolution crystal structures of internalins and internalin-like proteins from L. monocytogenes. Common to all these proteins is the presence of a so-called leucine-rich repeat (LRR) domain that specifically interacts with host cell receptors during invasion. The structure of the complex between the receptor-binding domain of internalin A and the N-terminal domain of human E-cadherin (Schubert, 2002) provided a detailed picture of the first step of listerial infection in the human intestine. It also explained the known host tropism of L. monocytogenes towards humans but not mice. For further information and follow-up projects see this link.
Recently we have solved the structure of the complex between second listerial invasion protein InlB with its human receptor Met, the natural tyrosine kinase receptor of hepatocyte growth factor/scatter factor (HGF/SF), which initiates uptake of the bacteria by many different tissues. The structure shows that InlB predominantly interacts via its LRR-domain with the Ig1-domain of Met in constrast to HGF/SF which targets the N-terminal Sema-domain (Niemann, 2007). We are currently investigating how the InlB-Met-interaction leads to uptake of the bacteria by the host.
Type III secretion system chaperones and effectors
We are working on several components, effectors and chaperones of the Y. enterocolotica type III and enteropathogenic Escherichia coli (EPEC) secretion systems. For efficient secretion, type III secretion system effectors require specific chaperone proteins that keep the effectors in a partially unfolded state prior to transfer through the injectisome.
After having solved the structure of the YopT chaperone SycT (Büttner et al, 2005) we recently solved the structure of SycD, which is responsible for translocator proteins showing a tetratricopeptide repeat fold (Heinz, 2007, in press) .
EPEC exploits the human adapter protein Nck as part of its infection strategy. During infection Nck specifically recognizes the phosphorylated translocated intimin receptor (Tir) which is inserted into the host membrane and eventually leads to dynamic bacteria-presenting protrusions of the plasma membrane known as pedestals. Using surface plasmon resonance spectroscopy, peptide epitope scanning and crystal structure determination of the Nck1 and Nck2 SH2-domains in complex with Tir-derived phosphopeptides we were able to investigate and differentiate the phosphopeptide binding affinities of Nck1 and Nck2 (Frese et al., 2006).
Enzymes of tetrapyrrole biosynthesis
The tetrapyrrole biosynthesis is a ubiquitous and central anabolic pathway leading to the formation of essential tetrapyrroles such as heme, chlorophyll and vitamin B12 from simple precursors. In a long-standing collaboration with Dieter Jahn (Technical University Braunschweig) we are systematically investigating the structural and functional elucidation of enzymes belonging to this pathway.
Recent examples are the structures of coproporphyrinogen IX oxidase and aminolevulinic acid synthase.
The O2-independent coproporphyrinogen IX oxidase represents the first structure of an enzyme belonging to the ubiquitous family of "Radical SAM enzymes". Our future goal is to elucidate the catalytic mechanism of this complicated enzyme from structural studies, as well as site-directed mutagenesis and use of synthetic inhibitors (in cooperation with Markus Kalesse, University of Hannover/HZI). (Layer et al, 2006)
Finally we have solved and analyzed the crystal structure of aminolevulinic acid synthase, the first enzyme of tetrapyrrole biosynthesis in mammals and yeast, in complex with both substrates. Mutations in this enzyme lead to rare blood disorders and other diseases. With the structure of aminolevulinic acid synthase the structures of all enzymes of heme biosynthesis have finally been determined. (Astner et al, 2005).
Future research will focus on the catalytic mechanism and substrate binding of selected enzymes.
