Parkinson's disease (PD) is a major cause of morbidity and mortality in the United States. The etiology is largely unknown and therapies that slow or halt the relentless progression of disease do not yet exist. Dominant missense mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common known specific cause of PD, and LRRK2 mutations associate with disease phenotypes that mimic typical late-onset disease. LRRK2 encodes an unusually large protein kinase, and the most common mutations that cause PD may up-regulate LRRK2 kinase activity. Since small molecule protein kinase inhibitors have made an impact on the treatment of multiple types of cancer, LRRK2 represents a potential therapeutic target for the treatment of PD should kinase activity correlate with neurodegeneration in model systems. Through the design of novel high capacity viral vectors encoding the LRRK2 open-reading frame modified with either PD-causing mutations that up-regulate kinase activity or mutations that inactivate kinase activity, the importance of LRRK2 kinase activity in directing dopaminergic neurodegeneration in vivo will be determined. The specific effects of pathogenic mutations on LRRK2 function and activity are not fully understood, but may allow for a straightforward route to decipher disease-related LRRK2 functions. LRRK2 encodes an active kinase and GTPase protein, a near unique arrangement in the human proteome, and pathogenic mutations can occur in both enzymatic domains. Oligomerization and dimerization are intrinsic mechanisms of regulation for many protein kinases and GTPase proteins. We will biochemically characterize oligomeric and dimeric LRRK2 protein and determine the effect of pathogenic LRRK2 mutations on the composition of LRRK2 conformations and associated activities. Further, we develop technology that may allow direct visualization of LRRK2 enzyme activity in living cells and explore both inhibition and activation of kinase activity. Through the resolution of LRRK2 autophosphorylation sites, we have uncovered an unexpected complexity in the probable reciprocal regulation of kinase and GTPase activities, where kinase activity may play a dual role in mediating GTPase-dependent LRRK2 dimerization and kinase-mediated phosphorylation of substrates. We will characterize the role of LRRK2 autophosphorylation on enzymatic regulation and how PD-associated mutations perturb normal activities.
The biochemical mechanisms underlying disease-causing mutations in the LRRK2 gene, currently the most common known cause of Parkinson's disease, are explored in order to determine potential targets for therapeutics development. Identification of cellular pathways linked with LRRK2-mediated neurodegeneration will further enhance our understanding of Parkinson's disease and spur the development of rationally designed drugs that slow or halt the disease.
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