Phosphorylation of a C-terminal auto-inhibitory domain increases SMARCAL1 activity

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• SMARCAL1 (homologous recombination repair protein) is essential for repairing damaged DNA replication forks.
• Dysregulation of SMARCAL1, through overexpression or silencing, leads to DNA damage accumulation.
• SMARCAL1 undergoes extensive phosphorylation, suggesting regulatory roles.

Purpose of the Study:

• To identify and characterize key phosphorylation sites regulating SMARCAL1 activity.
• To investigate the functional significance of S889 phosphorylation in DNA repair and replication fork stability.

Main Methods:

• Phosphoproteomic analysis to identify phosphorylation sites.
• Site-directed mutagenesis to create phosphomimetic and non-phosphorylatable S889 mutants.
• In vitro assays measuring ATPase activity and replication fork regression.
• Cellular assays to assess DNA damage and protein activity.

Main Results:

• Multiple SMARCAL1 phosphorylation sites were identified, with S889 being constitutively phosphorylated.
• S889 phosphorylation is conserved and enhances SMARCAL1's DNA-stimulated ATPase and fork regression activities.
• A phosphomimetic S889 mutant showed hyperactivity, while a non-phosphorylatable mutant was less active.
• Deletion of the C-terminal region, containing S889, also resulted in a hyperactive protein, suggesting S889 phosphorylation relieves auto-inhibition.

Conclusions:

• S889 phosphorylation is a key regulatory mechanism controlling SMARCAL1 activity.
• This phosphorylation enhances SMARCAL1's role in replication fork remodeling, essential for maintaining genome integrity during DNA synthesis.