From Promiscuity to Precision: Protein Phosphatases Get a Makeover David M. Virshup, Shirish Shenolikar  Molecular Cell  Volume 33, Issue 5, Pages 537-545 (March 2009) DOI: 10.1016/j.molcel.2009.02.015 Copyright © 2009 Elsevier Inc. Terms and Conditions

Figure 1 Regulation of Protein Phosphatase 1 (A) Protein phosphatase 1 is controlled by regulatory interactions (green) and inhibitors (red). Of the potentially hundreds of interactions between PP1 and cellular proteins, only a subset are depicted in this representation. (B) Regulatory interactions control the access of substrate to the catalytic site. Protein phosphatase 1δ (confusingly also named PP1β) is shown without (upper) and with MYPT1 subunit (PDB 1S70, Terrak et al., 2004). The catalytic metals in the active site are shown in yellow, PP1 with electrostatic potential, and MYTP1 in green. Note the interaction of MYPT1 with PP1 stabilizes its otherwise flexible or mobile C terminus, which is an extension of the globular core of the PP1 catalytic subunit. (C) A PP1 inhibitor physically blocks the active site. PP1γ1 without or with inhibitor-2 is shown with the catalytic subunits illustrated with surface electrostatic potential. I-2 is depicted in orange (PDB 2O8G, Hurley et al., 2007). The structures were displayed in MacPyMol (Delano, 2008). Molecular Cell 2009 33, 537-545DOI: (10.1016/j.molcel.2009.02.015) Copyright © 2009 Elsevier Inc. Terms and Conditions

Figure 2 The Diversity and Complexity of PP2A Numerous mechanisms control PP2A. Left: PP2A exists predominantly as a heterotrimer, with conserved A and C subunits and variable B subunits. This heterotrimer is regulated at multiple levels, including regulation of heterotrimer assembly, microbial toxins (such as okadaic acid and microcystin), protein inhibitors such as SET and CIP2A, and phosphorylation of the B and C subunits to regulate activity, assembly, and targeting. Right: the B subunits are encoded by at least 15 different genes, each with multiple splice variants. Molecular Cell 2009 33, 537-545DOI: (10.1016/j.molcel.2009.02.015) Copyright © 2009 Elsevier Inc. Terms and Conditions

Figure 3 The Structural Basis of Substrate Recognition by PP2A The B subunits of PP2A control localization and the access of substrates to the catalytic pocket. Each ABC heterotrimer will have a different substrate interface. Upper row: heterotrimeric ABαC, PDB 3DW8 from Xu et al. (2008) is shown on the left, and AB56γC, PDB 2IAE from Cho and Xu (2007) on the right. The A subunit is in red, the C subunit is in green, and the B subunit is in shades of blue. The catalytic metals in the C subunit are difficult to see in this projection but are highlighted in yellow. The phosphatase inhibitor and toxin microcystin, bound in the active site, is shown in orange. In the ABαC structure, the residues in Bα determined to be critical for dephosphorylation of Tau are highlighted in pink. These residues contact the substrate and position it for dephosphorylation (Xu et al., 2008). The Bα residues that are different in the closely related Bδ subunit are shown in yellow. These sequence variations lie some distance from the catalytic site and may, therefore, regulate targeting interactions rather than mediate direct substrate binding. Lower row: the cartoon shows how the B subunits might shape and restrict access to the catalytic pocket allowing specific substrates, and specific phosphorylation sites, to be dephosphorylated. The structures were displayed in MacPyMol (Delano, 2008). Molecular Cell 2009 33, 537-545DOI: (10.1016/j.molcel.2009.02.015) Copyright © 2009 Elsevier Inc. Terms and Conditions