Summary Protein function originates from a cooperation of structural rigidity, dynamics at different timescales and allostery. However, how these three pillars of protein function are integrated is still only poorly understood. Here we show how these pillars are connected in Protein Tyrosine Phosphatase 1B (PTP1B), a drug target for diabetes and cancer that catalyzes the dephosphorylation of numerous substrates in essential signaling pathways. By combining new experimental and computational data on wt-PTP1B and ≥10 PTP1B variants in multiple states, we discovered a fundamental and evolutionarily conserved CH/π switch that is critical for positioning the catalytically important WPD loop. Furthermore, our data show that PTP1B uses conformational and dynamic allostery to regulate its activity. This shows that both conformational rigidity and dynamics are essential for controlling protein activity. This connection between rigidity and dynamics at different timescales is likely a hallmark of all enzyme function.

The serine/threonine protein phosphatase 1 (PP1) dephosphorylates hundreds of key biological targets by associating with nearly 200 regulatory proteins to form highly specific holoenzymes. However, how these proteins direct PP1 specificity and the ability to predict how these PP1 interacting proteins bind PP1 from sequence alone is still missing. PP1 nuclear targeting subunit (PNUTS) is a PP1 targeting protein that, with PP1, plays a central role in the nucleus, where it regulates chromatin decondensation, RNA processing, and the phosphorylation state of fundamental cell cycle proteins, including the retinoblastoma protein (Rb), p53, and MDM2. The molecular function of PNUTS in these processes is completely unknown. Here, we show that PNUTS, which is intrinsically disordered in its free form, interacts strongly with PP1 in a highly extended manner. Unexpectedly, PNUTS blocks one of PP1's substrate binding grooves while leaving the active site accessible. This interaction site, which we have named the arginine site, allowed us to define unique PP1 binding motifs, which advances our ability to predict how more than a quarter of the known PP1 regulators bind PP1. Additionally, the structure shows how PNUTS inhibits the PP1-mediated dephosphorylation of critical substrates, especially Rb, by blocking their binding sites on PP1, insights that are providing strategies for selectively enhancing Rb activity.nuclear phosphatases | enzyme regulation | enzyme specificity | X-ray crystal structure | nuclear magnetic resonance P rotein phosphatase 1 (PP1; ∼38.5 kDa), a single-domain protein, is the most widely expressed and abundant serine/threonine phosphatase (1). By dephosphorylating a variety of protein substrates, PP1 regulates diverse biological processes, including protein synthesis, muscle contraction, carbohydrate metabolism, neuronal signaling and, of specific interest for this work, cell-cycle progression. Although the intrinsic substrate specificity of PP1 is very low, by interacting with regulatory proteins (∼200 biochemically confirmed PP1 interactors), PP1 achieves high specificity (2-5). The majority of PP1 regulators and some substrates bind PP1 via a primary PP1-binding motif, the RVxF motif, which binds to a hydrophobic groove on PP1 ∼20 Å distal from its catalytic center (6). Outside of the RVxF motif, PP1 regulatory proteins mostly lack any apparent sequence similarity. Thus, additional interaction sites, such as the SILK (7), the MyPhoNE (8), and the recently identified ΦΦ motif (9) can only be identified by structural analysis, a major challenge for a comprehensive understanding of PP1 regulation. Only when the primary sequences of PP1 regulators are correlated with specific PP1 binding modes and activities will the PP1 interactome, and the biological processes it regulates, become a viable drug target for the multitude of PP1-associated diseases, such as multiple cancers.One of the key PP1 regulatory targeting proteins in the nucleus, in addition to nuclear inhibitor of PP1 (NIPP1) and Repoman, is the...

Summary The attenuation of protein synthesis via the phosphorylation of eIF2α is a major stress response of all eukaryotic cells. The Growth Arrest and DNA-damaged protein 34 (GADD34) bound to the serine/threonine protein phosphatase 1 (PP1) is the necessary eIF2α phosphatase complex that returns mammalian cells to normal protein synthesis following stress. The molecular basis by which GADD34 recruits PP1 and its substrate eIF2α are not fully understood, hindering our understanding of the remarkable selectivity of the GADD34:PP1 phosphatase for eIF2α. Here we report detailed structural and functional analyses of the GADD34:PP1 holoenzyme and its recruitment of eIF2α. The data highlight independent interactions of PP1 and eIF2α with GADD34, demonstrating that GADD34 functions as a scaffold both in vitro and in cells. This work greatly enhances our molecular understanding of a major cellular eIF2α phosphatase and establishes the foundation for future translational work.