Deciphering the LRRK code: LRRK1 and LRRK2 phosphorylate distinct Rab proteins and are regulated by diverse...

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Mutations in Leucine-rich repeat kinase 2 (LRRK2) are linked to Parkinson's disease, with LRRK2 phosphorylating Rab GTPases like Rab8A and Rab10.
• LRRK1, a homolog of LRRK2, is involved in growth factor receptor trafficking and osteoclast biology, but its role in Rab protein phosphorylation is less understood.

Purpose of the Study:

• To investigate whether Leucine-rich repeat kinase 1 (LRRK1) phosphorylates Rab proteins.
• To identify the specific Rab proteins and phosphorylation sites targeted by LRRK1.
• To explore the functional consequences and regulation of LRRK1-mediated phosphorylation.

Main Methods:

• Mass spectrometry was used to analyze Rab protein phosphorylation in LRRK1 knock-out cells.
• Recombinant LRRK1 was used to test direct phosphorylation of Rab proteins.
• A novel phospho-specific antibody was developed to detect Rab7A phosphorylation at Ser72 in stimulated cells.

Main Results:

• LRRK1 knock-out cells showed significantly impacted phosphorylation of Rab7A at Ser72, a site homologous to LRRK2 targets.
• Recombinant LRRK1 efficiently phosphorylated Rab7A at Ser72, but not Rab8A or Rab10.
• Two LRRK1 mutations, K746G and I1412T, enhanced LRRK1-mediated Rab7A phosphorylation, analogous to Parkinson's-associated LRRK2 mutations.

Conclusions:

• LRRK1 is identified as a kinase that phosphorylates Rab7A at Ser72, demonstrating distinct substrate specificity compared to LRRK2.
• The findings suggest that LRRK enzymes have evolved as crucial regulators of Rab biology with specialized substrate preferences.
• This study expands the understanding of LRRK kinase function beyond Parkinson's disease associations, revealing a novel regulatory pathway for Rab7A.