LRRK2 mutations are commonly associated with inherited Parkinsons disease and one mutation (G2019S) is known to increase the kinase activity of the protein. As such, there have been several recent publications exploring this activity as a potential therapeutic target in PD. The goal of this project is to understand the kinase activity by identifying substrates for LRRK2. We have explored how recombinant LRRK2 phosphorylates several reported substrates from the literature. We found that data on two of them (4EBP and MKK6) can be replicated but in both cases phosphorylation of the proposed substrates by LRRK2 is relatively weak. In the case of 4EBP we did not find evidence for phosphorylation of LRRK2 in cells, even when LRRK2 is overexpressed. In both cases, we found that LRRK2 will phosphorylate itself more efficiently than exogenous proteins. To further characterize this phenomenon, we mapped the autophosphorylation of LRRK2 and, surprisingly, saw that LRRK2 can modify a second region of itself, the ROC (for ras of complex proteins) or GTPase region. This is potentially important as mutations associated with Parkinsons disease are found in both the kinase and ROC domains and thus autoregulation may be a simple explanation as to how multiple mutations impact the same protein to cause disease. However, we are still trying to confirm that these sites are authentically modified in vivo.
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