Substrate displacement of CK1 C-termini regulates kinase specificity

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Signaling

Background:

• Casein kinase 1 (CK1) enzymes are crucial regulators in diverse cellular signaling pathways.
• CK1s possess C-terminal noncatalytic tails that undergo autophosphorylation.
• Autophosphorylation of these tails is hypothesized to inhibit kinase activity by acting as pseudosubstrates.

Purpose of the Study:

• To investigate the regulatory role of C-terminal autophosphorylation in CK1 activity and substrate specificity.
• To identify and characterize autophosphorylation sites in *Schizosaccharomyces pombe* Hhp1 and human CK1ε.

Main Methods:

• Comprehensive identification of autophosphorylation sites.
• Utilizing phosphoablating mutations to assess kinase activity.
• Investigating the interaction between C-terminal peptides, kinase domains, and substrates using biochemical assays.
• Analyzing the effect of tail truncation on substrate specificity.

Main Results:

• Phosphoablating mutations significantly increased the catalytic activity of Hhp1 and CK1ε towards substrates.
• Phosphorylated C-terminal peptides bound to kinase domains, and this binding was competitively inhibited by substrates.
• Tail autophosphorylation modulated the catalytic efficiency for different substrates.
• Truncation of the CK1δ tail expanded its substrate motif, indicating a role in substrate specificity.

Conclusions:

• C-terminal autophosphorylation of CK1s functions as an inhibitory mechanism.
• Autophosphorylated C-terminal tails act as pseudosubstrates that bind to the kinase domain.
• CK1 tails contribute to substrate specificity, and autophosphorylation modulates this specificity.
• A displacement specificity model is proposed to explain autophosphorylation's role in CK1 substrate specificity.