Parkinson Disease (PD) is the second most common neurodegenerative disorder, significantly impairing motor skills but also non-motor functions. It is characterized by a progressive loss of midbrain dopaminergic neurons in the substantia nigra, leading to dopamine depletion in the striatum. Besides the sporadic form of PD (idiopathic PD) characterized by a complex etiology and the absence of a clear pattern of inheritance, familial forms exist which are caused by single gene defects.
One of these genes is the leucine-rich repeat kinase 2 (LRRK2), the most prevalent gene associated with PD. Mutations within LRRK2 show a dominant mode of inheritance and account for up to 10% of the familial PD cases. The LRRK2 protein belongs to the ROCO protein superfamily and possesses a complex domain composition that comprises both an active kinase and GTPase domain as well as regulatory and protein interaction domains. However, little is known about the involvement of LRRK2 in the molecular pathogenesis of PD. In projects funded by NGFN-Plus, the Helmholtz Alliance for Mental Health in an Ageing Society and the Michael J. Fox Foundation, we employ biochemical, cell biological and biophysical approaches as well as structural biology techniques (NMR and/or X-ray crystallography - in cooperation with Michael Sattler and Peijian Zou, ISB) to investigate the molecular basis of LRRK2’s physiological and pathophysiological function.
Given that the kinase domain (mitogen-activated protein kinase kinase kinases, MAPKKK) as well as the Ras-like GTPase (Ras of complex protein, Roc) domain are affected by several pathogenic mutations and MAPKKKs play a central role in mediating cellular stress events, one focus of our work is to analyze and characterize the kinase and GTPase activity of Lrrk2. Indeed, recent studies, including our own work (Gloeckner et al., Hum Mol Genet. 2006), point towards an increase of LRRK2 kinase activity caused by PD-associated mutations. The presence of domains showing high similarity to well defined protein interaction domains (i.e. leucine rich repeats (LRR) and WD40) suggests that protein-protein interactions could be crucial for the biological function of LRRK2. Thus, the molecular interactome of LRRK2 is currently systematically analyzed. Based on a lentiviral gene transfer system (Bauer et al., Gene Ther. 2009), primary neuronal cell culture models have furthermore been established that allows a targeted knockdown of LRRK2 by shRNA expression.
These cell culture models combined with structural and biochemical analyses will contribute to a molecular understanding of both LRRK2-related cellular pathways as well as the implications of disease-linked mutations on the protein’s function, thus providing insight into the role of LRRK2 in neuronal physiology and PD etiology. Furthermore, the structural data can assist the design of inhibitors towards the identification of new drugs against PD (together with Boehringer Ingelheim CNS Research, Biberach).