Structural comparison of CLKs. (a) The superimposed structures of CLK1/CX-4945, CLK2/CX-4945, and CLK3/CX-4945 indicated three discrete parts; the N- and C-termini are indicated as I and II (black boxes). The CLK1 and bound CX-4945 molecules are colored in cyan and blue, respectively. The CLK2 and bound CX-4945 molecules are colored in light green and green, respectively. The CLK3 protein and CX-4945 ligand are colored in pink and magenta, respectively. (b) The 90° rotated view along the Y-axis from (a) is shown with the varied β-hairpin insertion conformations indicated as III (black box).