Full-length LRRK2 activation cycle and dimer-monomer equilibrium
Mutations in the Leucine-rich repeat Kinase 2 (LRRK2) gene have been identified as associated with Parkinson's disease (PD). Previous biochemical and cellular data indicated LRRK2 protein cycles between a monomeric cytosolic state with low kinase activity and a highly active oligomeric membrane-bound state. The bacterial homolog protein, Chlorobium tepidum Roco showed a monomer-dimer transition during GTP turnover. However, the intra-molecular regulation and monomer-dimer transition of LRRK2 are still unclear.
In her thesis, with the integration of biochemical methodologies and molecular modeling techniques, Xiaojuan Zhang elucidates that Methanosacrcina barker (Mb) RocCOR, another bacterial homolog protein, also undergoes a monomer-dimer transition during hydrolysis, and the PD analogous (Y1699C) shows a faster monomer-dimer turnover than the wild-type. LRRK2 RocCOR domain has a GTPase activity in a similar range as full-length LRRK2 and exists in monomeric and dimeric form, and the PD-related mutation Y1699C might influence the monomer/dimer equilibrium. Additionally, Zhang found that LRRK2 autophosphorylation can induce monomerization and consequentially negatively regulate GTP hydrolysis. Through systematic mutational analysis, she identified the T1343 in the P-loop motif is critical in this feedback. Inhibiting LRRK2 dimerization by stapled peptide to attenuate the monomer/dimer cycle can effectively attenuate kinase activity and reduce LRRK2 PD-mediated neuronal apoptosis. Altogether, Zhang's findings indicated the monomer-dimer equilibrium is a key step in LRRK2 activation, and the PD mutants might be mediated by distinct pathophysiological mechanisms.