Fig. 4: PP2A:B55 preferentially dephosphorylates p107 CDK2–cyclin A2 phosphosite pS640.
From: Cryo-EM structures of PP2A:B55 with p107 and Eya3 define substrate recruitment
a, PP2A:B55–p107 showing that p107 (salmon, shown as sticks) binds the B55 platform (beige) and wall (green). B55 interaction pockets occupied by p107 are labeled and their positions are indicated by arrows. Key p107 interacting residues are labeled. The interaction sequence is shown below, with residues that mediate intermolecular contacts underlined and those important for intramolecular contacts in italics. b, p107 L617 (salmon) binds the B55 P7 hydrophobic pocket (P5 pocket residues shown as sticks). c, p107 H619 (salmon) binds the B55 P8 hydrophobic/polar pocket (P6 pocket residues are shown as sticks; polar interactions are shown with a black dotted line). d, Overlay of p107 (salmon) and the FAM122A B55-binding helix (orange), with side chains shown as sticks. Structural alignment of p107 and FAM122A interacting residues are also shown. e, p107 R621 (salmon) binds the B55 P4 acidic pocket (P4 pocket and key p107 residues are shown as sticks; the multiple intermolecular and intramolecular interactions that stabilize the conformation are shown as black dotted lines). f, p107 V622 and V625 bind the B55 hydrophobic P2 and P1 pockets (P1 and P2 pocket residues are shown as sticks), respectively, while p107 R626 binds the hydrophobic/polar P3 pocket (P3 pocket residues are shown as sticks, with hydrogen bonds between R626 and the 222MEELT226 carbonyls indicated by dashed lines). g, PP2A:B55 inhibition by p107 and Eya3 (mean ± s.d.; n = 3 experimental replicates). IC50 values are reported in Extended Data Table 1. h, Cartoon illustrating p107 phosphorylation (CDK2 and cyclin A2) and subsequent time course of dephosphorylation (PP2A:B55) assays. i, The 2D [1H,15N] HSQC spectrum of 15N-labeled unphosphorylated p107 (black) overlaid on CDK2–cyclin A2-phosphorylated 15N-labeled p107 (purple); S615 and S640 are phosphorylated, with shifted peaks labeled. j–n, The 2D [1H,15N] HSQC spectra of unphosphorylated 15N-labeled p107 (black) overlaid with on CDK2–cyclin A2-phosphorylated 15N-labeled p107 incubated with PP2A:B55 (red) at time points of 45 min (j), 129 min (k), 213 min (l), 409 min (m) and 1,277 min (n). o, Changes in peak intensities of 15N-labeled p107 residues pS640 (red) and S640 (black).
