Control experiment verifying the specificity of the mutation-directed crosslinking reaction.

(A) Crystal structure of SRPK1 in complex with a 9-mer peptide (PDB ID: 1WBP). The binding interface of the docking groove of SRPK1 and the 9-mer peptide that mimics a substrate docking motif is shown (right). (B) Crystal structure of SRPK1 in complex with SRSF1 (PDB ID: 3BEG). The binding interface of the docking groove of SRPK1 and the N’-RS1 of SRSF1 is shown (right). (C) CpY132A(surface C to S), with all surface-exposed cysteine residues mutated, was used as a control for the chemical crosslinking. Reactions were performed in the presence of increasing concentrations of ATP. The molar ratio of ATP to Cp is indicated. SDS-PAGE analysis showed that CpY132A(surface C to S) did not non-specifically crosslink with SRPK2ΔS1(K648C).

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