Currently, we aim to elucidate the structural determinants of the immune defense mechanisms by NODlike receptors (NLRs) in infectious processes. Moreover, we want to analyse how pathogens inhibit NODlike receptors upon infection to evade the host's defence. The cytosolic NLRs trigger the inflammatory response in reaction to pathogen- or danger-associated signals. NLRs of the NLRP subfamily oligomerize upon activation into large multimers called inflammasomes. An inflammasome comprises several copies of a sensor component such as NLRP3 (NLR family protein containing a pyrin domain 3), the adaptor ASC (apoptosis-associated speck-like protein containing a caspase activation and recruitment domain), and the effector pro-caspase 1.
The transition from inactive monomer to active oligomer is characteristic for NOD proteins, to which also NLRPs belong, and has been described by us in molecular detail for the NOD protein Apaf-1, the key switch in the mitochondrial pathway of apoptosis. Combining structural information from the X-ray structure of auto-inhibited Apaf-1 and the cryo-EM structure of the apoptosome, we depicted the conformational changes of Apaf-1, which eventually lead to the transduction of the cellular death signal.
To understand the dynamics of the activation of NLRPs, we structurally analyse the monomeric start states and the oligomeric end states of the activation process for several of the receptors. To depict the end states, the methods of choice are, up to now, cryo-EM of the multimer in combination with X-ray crystallographic analysis of autoinhibited monomers or subdomains of NLRPs.
A second core research area in our current research portfolio is the work on the large GTPase dynamin. Dynamin is a key protein in clathrin mediated endocytosis and numerous other membrane remodeling processes. Moreover, dynamin is a promising target for therapeutic intervention in chronic kidney diseases (CKDs). We want to provide the basis for novel strategies to treat CKDs in collaboration with Prof. Dr. Mario Schiffer from the University Hospital in Erlangen.
Dynamin is the target of the small molecule Bis-T23, which has been shown to restore proper kidney function in proteinuric zebrafish and mice. Bis-T23 stimulates oligomerization of dynamin through direct interaction, which in turn leads to repair of the actin cytoskeleton in the visceral glomerular epithelial cells of the kidney (podocytes). We aim to depict the binding mode of Bis-T23 to dynamin by X-ray crystallographic analysis of dynamin in complex with Bis-T23 for rational modification of Bis-T23 or the rational design of new compounds. We have determined the crystal structure of the human dynamin tetramer (Reubold et al. 2015, Nature), which represents the key state of the oligomerization cycle of dynamin. The structure fully describes the interface that is responsible for the assembly of higher-order oligomers of dynamin. We suppose that binding of Bis-T23 facilitates the formation of this oligomerization interface. Therefore, the dynamin tetramer is a very good starting point for soaking experiments with Bis-T23 and in silico searches for other compounds that may also trigger dynamin oligomerization.