Substrate phosphorylation of protein microarray by leucine-rich repeat kinase 2

Numerous leucine-rich repeat kinase 2 mutations identified throughout the protein are associated with Parkinson disease, however the activating G2019S kinase domain mutation is currently regarded as the most common cause of familial and sporadic forms of this disorder. Despite studies demonstrating the prominent role that its kinase activity plays in the pathobiology of leucine-rich repeat kinase 2, few substrates have been identified and only a subset of these have been linked to disease. Therefore, we utilized protein microarrays to screen over 9,000 human proteins in an unbiased radiometric assay for potential targets of the kinase. ProtoArray™ Human Protein Microarrays v5.0 (Invitrogen, Carlsbad, CA, USA) were used following the manufacture’s protocol (ProtoArray Kinase Substrate Identification Kit). Briefly, slides were equilibrated at 4C for 15 min before blocking in 1% BSA in PBS for 1 h at 4oC with gentle shaking. Recombinant G2019S or D1994A glutathione-S-transferase (GST)-LRRK2 (970-2527) (Invitrogen) was diluted to 50nM in 20mM Tris (pH 7.5), 10mM MgCl2, 1mM EGTA, 1mM Na3VO4, 5mM beta-glycerophosphate, 2mM DTT, 0.02% polysorbate 20, and 10 mCi /mL of [gamma- 33P]ATP (33 nM final concentration) in a total volume of 120uL. Slides were overlayed with buffer alone, or buffer containing G2019S or D1994A LRRK2, then covered with a coverslip and placed in a 50 mL conical tube for 1 h at 30oC. Afterwards, slides were washed with 0.5% SDS buffer and water followed by centrifugation. Dried slides were exposed to a PhosphorImager plate (Amersham Biosciences, Piscataway, NJ, USA), and scanned on a Storm 840 (Molecular Dynamics, Inc., Sunnyvale, CA, USA) at 50 microns.