Extended Data Fig. 9: Intra- and intermolecular PP2A:B55-inhibitor interactions.

a. The methylated C-terminal tail of PP2Ac (cyan) extends to the opposite side of PP2A (grey) where it interacts at the interface between PP2Aa and B55 (lavender). b. Close-up of (a) with the C-terminus shown as sticks and PP2Aa, B55 and the rest of PP2Ac shown as a surface. c. Different view of a,b with the PP2Ac C-terminus shown as sticks and PP2Aa and B55 interacting residues also shown as sticks. Polar/ionic inter-subunit interactions indicated by black dashed lines and the participating residues underlined. d. Detailed interactions between the methylated C-terminal tail of PP2Ac (cyan, highlighted by purple box in (a)) with PP2Aa (grey) and B55 (lavender). e. Alanine scanning mutagenesis of ARPP19 amino acids L32-Q41. The indicated YFP-ARPP19 constructs were transfected into HeLa cells and immunopurified. Binding efficiency of the YFP-ARPP19 derivatives to B55 and PP2Ac was determined by Western blotting. f. Quantification of (e) based on two independent experiments. g. Alanine scanning mutagenesis of ARPP19 amino acids D47-G56. The indicated YFP-ARPP19 constructs were transfected into HeLa cells and immunopurified. Binding efficiency of the YFP-ARPP19 derivatives to B55 and PP2Ac was determined by Western blotting. Quantification of (g) based on two independent experiments shown in Fig. 3e. h. FAM122A K89 makes polar/ionic interactions (dashes) with multiple residues from B55. i. Helical wheel N→C view of the B55 inhibition helix highlighting residues that interact with PP2Ac and those that are solvent exposed.