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Splicing requires reversible phosphorylation of serine/arginine-rich (SR) proteins, which direct splice site selection in eukaryotic mRNA. These phosphorylation events are dependent on SR protein (SRPK) and cdc2-like kinase (CLK) families. SRPK1 phosphorylation of splicing factors is restricted by a specific docking interaction whereas CLK activity is less constrained. To understand functional differences between splicing factor targeting kinases, we determined crystal structures of CLK1 and CLK3. Intriguingly, in CLKs the SRPK1 docking site is blocked by insertion of a previously unseen helix alphaH. In addition, substrate docking grooves present in related mitogen activating protein kinases (MAPKs) are inaccessible due to a CLK specific beta7/8-hairpin insert. Thus, the unconstrained substrate interaction together with the determined active-site mediated substrate specificity allows CLKs to complete the functionally important hyperphosphorylation of splicing factors like ASF/SF2. In addition, despite high sequence conservation, we identified inhibitors with surprising isoform specificity for CLK1 over CLK3.

Original publication

DOI

10.1016/j.str.2008.12.023

Type

Journal article

Journal

Structure

Publication Date

11/03/2009

Volume

17

Pages

352 - 362

Keywords

Amino Acid Sequence, Binding Sites, Humans, Models, Molecular, Molecular Sequence Data, Mutagenesis, Insertional, Nuclear Proteins, Phosphorylation, Protein Conformation, Protein Structure, Tertiary, Protein-Serine-Threonine Kinases, Protein-Tyrosine Kinases, RNA Splicing, RNA-Binding Proteins, Serine-Arginine Splicing Factors, Substrate Specificity