Most eukaryotic proteins are regulated by phosphorylation. Phosphoprotein phosphatases (PPPs) are the key serine/threonine phosphatases that regulate all essential signaling cascades. In particular, Protein Phosphatase 1 (PP1) dephosphorylates a predicted ~80% of all ser/thr phosphorylation sites. Here, we developed a phosphatase targeting peptide (PhosTAP) that binds all PP1 isoforms and does so with a stronger affinity than any other known cognate PP1 regulator. This PhosTAP can be used as a PP1 recruitment tool for PhosTAC-type recruitment in in vitro and cellular experiments, as well as in phosphoproteomics experiments to identify PP1-specific substrates and phosphosites. The latter is especially important to further our understanding of cellular signaling, as the identification of substrates and especially phosphosites that are targeted by specific phosphatases, like PP1, lags far behind that of their kinase counterparts. This is due to a lack of chemical/biological tools that are specific for individual phosphatases and a lack of established active site recognition sequences. Using PhosTAP-based proteomics studies, we show that, counter to our current understanding, many PP1 regulators are also substrates; that the number of residues between regulator PP1-binding and phosphosites vary significantly; and that PP1 also counteracts the activities of mitotic kinases. Finally, we also discovered that Haspin kinase is a direct substrate of PP1 and that its PP1-dependent dephosphorylation modulates its activity during anaphase. Taken together, we show that PP1-specific PhosTAPs are a powerful tool for studying PP1 activity in vitro and in cells.
[doi:10.25345/C5N01048F]
[dataset license: CC0 1.0 Universal (CC0 1.0)]
Keywords: phosphoprotein phosphatase ; PPP ; PP1 ; PhosTAP ; Haspin
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Arminja Kettenbach, The Geisel School of Medicine at Dartmouth, United States |
Submitting User: | madamo |
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