Constrained peptide mimics of the LRRK2 C-terminal Helix inhibits its kinase activity.

Leucine-rich repeat kinase 2 (LRRK2) is the most frequently mutated gene in Parkinson's disease (PD), a neurodegenerative disorder affecting over 10 million people. PD-related pathogenic mutations in LRRK2 increase its kinase activity, thereby contributing to disease pathology. While elevated LRRK2 activity is a recognized contributor to PD, the precise mechanisms by which its various domains regulate kinase activation remain unclear. To address this, we developed hydrocarbon-constrained peptides that mimic the C-terminal helix of LRRK2, a region implicated in modulating its kinase activity. These peptides are cell-penetrant, directly bind LRRK2, and inhibit kinase function. Consequently, they suppress downstream LRRK2-associated pathological phenotypes, including centrosomal and ciliary defects. Unlike many ATP-competitive LRRK2 inhibitors that induce LRRK2 mislocalization, these peptides do not alter LRRK2 localization. Our findings highlight a potentially critical regulatory role of the LRRK2 C-terminal helix and suggest a novel, alternative strategy for modulating pathogenic LRRK2 activity as relevant in PD.