Extended Data Figure 10: PP1-docking-site mutations do not alter the stoichiometry of PP2A subunits in immunoprecipitation assays or of holoenzymes isolated by TAP-tag purification. | Nature

Extended Data Figure 10: PP1-docking-site mutations do not alter the stoichiometry of PP2A subunits in immunoprecipitation assays or of holoenzymes isolated by TAP-tag purification.

From: A PP1–PP2A phosphatase relay controls mitotic progression

Extended Data Figure 10

ac, Immunoprecipitation reactions from cell extracts of the indicated strains in which the 12CA5 antibodies were used to precipitate epitope-tagged versions of the B55Pab1 or B56Par1 PP2A regulatory subunits or in which polyclonal antibodies against GFP were used to precipitate a GFP-tagged version of the APaa1 PP2A scaffolding subunit. Although mutation of either the PP1-docking site motif sequences or the B56par1.S378D mutation abolished PP1 precipitation with each PP2A holoenzyme, they had no impact upon the stoichiometry of PP2A subunits precipitating with either the regulatory or the scaffolding subunits. We conclude that the PP1-docking site mutations do not alter the integrity of the PP2A-B55 or PP2A-B56 holoenzyme complexes. The ability to detect S377/S378 phosphorylation in APaa1 precipitates consolidates the data in Extended Data Fig. 5g to demonstrate that this site between the two elements of the PP1-docking site of B56Par1 can be phosphorylated in the PP2A-B56Par1 holoenzyme complexes. Catalytic CPpa1 and CPpa2 and the scaffolding APaa1 subunits of PP2A were detected with commercial antibodies. d, The tandem affinity purification scheme used to isolate PP2A phosphatases from yeast cultures via the TAP tag fused to the scaffolding APaa1 subunit. e, Coomassie-stained 4–12% SDS–NUPAGE gradient gels of APaa1.TAP purifications of the indicated strains. The disappearance of bands upon gene deletion combined with mass spectrometric analysis of isolated bands after a further round of purification (Extended Data Fig. 5b, c) confirms that this procedure isolates PP2A enzymes. The persistence of the wild-type pattern in B55pab1.PDSN, B56par1.PDSN and B56par1.S378A strains indicates that these mutations do not alter the composition of either PP2A holoenzyme, that is, they do not alter the structural bonds that maintain the integrity of the PP2A holoenzyme complexes, as predicted from existing current crystal structures of PP2A holoenzyme complexes28,29,30. Biological replicates: for all panels, n = 2.

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