Fig. 5: FAM122A effectively competes binding to the holoenzyme, which is consistent with the AFM model predicting superimposition of the FAM122A and p107 SHeMs. | Nature Communications

Fig. 5: FAM122A effectively competes binding to the holoenzyme, which is consistent with the AFM model predicting superimposition of the FAM122A and p107 SHeMs.

From: FAM122A ensures cell cycle interphase progression and checkpoint control by inhibiting B55α/PP2A through helical motifs

Fig. 5: FAM122A effectively competes binding to the holoenzyme, which is consistent with the AFM model predicting superimposition of the FAM122A and p107 SHeMs.

A Purified PP2A/B55α holoenzymes were incubated with purified HA-FAM122A (expressed in E coli) starting with the same concentration as B55α in each sample up to a ~100X. B55α: R1R2 binding in GST-p107-R1R2 pull-downs was inhibited at the lowest FAM122A concentration. (n = 3). Source data are provided in the Source Data file. B Schematic interpretation of A. C Co-transfection of invariable amounts of Myc-B55α and FLAG-p107 plasmids with increased amounts of FAM122A, as indicated. (n = 3). Source data are provided in the Source Data file. Anti-Myc immunoprecipitates were analyzed by western blot and relevant proteins are indicated. D AlphaFold-Multimer model of superimposing a predicted helix containing the p107 with the predicted helix-1 of hFAM122A. Conserved SLiM residues in both proteins superimpose and make contacts with D197 and L225. Residue numbering corresponds to the human proteins. E GST-R1R2 constructs created with a single phosphosite (S615 or S640). Arginine to Alanine mutations disrupted the SLiM motif in the indicated constructs. Western blot visualization of time-dependent kinase-dephosphorylation assays of the R1R2 constructs. GST-R1R2 variant beads were phosphorylated with CDK1/cyclin B kinase. Washed phosphorylated beads were incubated with PP2A/B55α for the indicated times (n = 3). F Schematic representation of the substrate-competitive SHeM mechanism of inhibition, which involves the two helices. Helix-1 (SHeM) mediates binding to B55α and helix-2 acts as inhibitory flapper by directly contacting the active site.

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