Mutations in leucine-repeat rich kinase 2 (LRRK2) are the most common known cause of late-onset Parkinson's disease. In this study, a novel system to purify active recombinant LRRK2 expressed in mammalian cells was generated. This recombinant enzyme was used to characterize the specificity of LRRK2 and identify small compounds that can inhibit the kinase activity. Recombinant LRRK2 was shown to autophosphorylate and phosphorylate MBP and a peptide (LRRKtide) corresponding to the T688 site in moesin. A series of well-characterized kinase peptide substrates was not modified by LRRK2 demonstrating remarkable specificity. G2019S, the most common disease-causing mutation in LRRK2, increased kinase activity more dramatically than previously appreciated (similar to 10-fold). Several small molecules sharing a basic indolocarbazole structure (Go66976, K-252a, and staurosporine) where identified as potent inhibitors of LRRK2 kinase activity. These findings provide important insights and tools to Study the mechanisms of LRRK2 pathobiology, and could lead to therapeutic applications. (C) 2008 Elsevier Inc. All rights reserved.