DOC_CDC14_PxL_1

During the cell cycle, Cdk phosphorylation activity is modulated by opposing phosphatase activities. In budding yeast, Cdc14 acts as an antagonist of Cdk activity and a key regulator of late mitotic events such as chromosome segregation, spindle disassembly, and cytokinesis (Mocciaro,2010; Breitkreutz,2010). Cdc14 homologues have been identified in a wide range of organisms ranging from yeast to human. But the requirement of Cdc14 for mitotic exit is not conserved outside the budding yeast. The fission yeast Cdc14 homologue, Cdc14-like phosphatase 1 (Clp1; also known as Flp1) contributes to the control of cytokinesis, but is not required for other aspects of mitotic exit or Cdk1 inactivation. The nematode homologue, CDC-14 also plays a role in the regulation of cytokinesis. Among the three vertebrate paralogues (CDC14A, CDC14B, and CDC14C), the CDC14B appears to be the most functionally related to yeast Cdc14 and plays major roles in functions such as the G2/M DNA damage checkpoint, DNA repair and centrosome duplication, while CDC14A is involved in centrosome separation and cytokinesis, suggesting that the functions of CDC14 phosphatases have been partially rewired during eukaryotic evolution but preserve important roles in cell cycle and DNA damage regulation. In higher eukaryotes, the role of yeast Cdc14 is partly taken over by the PP1 and PP2A phosphatases (Wurzenberger,2011). The yeast dual-specificity phosphatase Cdc14 is sequestered in the nucleolus for most of the cell cycle by the nucleolar proteins Net1 and Tof2, and is only released into the nucleus and cytoplasm during anaphase (Visintin,1999; Shou,1999). In anaphase, the so called Fourteen Early Anaphase Release (FEAR) network (including Cdc5, Esp1, and Slk19), and the mitotic exit network (including the Dbf2-Mob1 complex) co-ordinately trigger the release of Cdc14 from the nucleolus (Shou,1999). Subsequently, Cdc14 performs the sequential dephosphorylation of its targets (Bouchoux,2011). Yeast Cdc14 forms a homodimer (5XW4; Kobayashi,2017). In vitro, Cdc14 strongly favours dephosphorylation of phosphoserines followed by a proline, with an additional positively charged residue downstream (SPxK/R) which, maybe not surprisingly, conforms to a Cdk consensus phosphorylation motif (Bremmer,2012). Phosphothreonines are poor Cdc14 substrates, due to a steric clash with the phosphatase active site (Bremmer,2012). The structure of the complex between Cdc14 and S-phosphorylated Swi6p peptide provides information on the catalytic mechanism of Cdc14 (5XW5). The non-catalytic, N-terminal pseudophosphatase domain (DSPn; Pfam:PF14671) of Cdc14 has a binding pocket that recognizes the PxL docking motif on its substrates (6G86; 6G85). This docking event enhances target recognition and dephosphorylation of both optimal and suboptimal targets, for example those containing phosphothreonines (Kataria,2018). A Cdc14 dimer can bind two of these motifs wherein the docking site of protomer 1 is much closer to the active site of protomer 2 than its own, implying that docking sites may regulate catalytic activity of the opposite protomer (Kataria,2018). The dimerization of Cdc14 is therefore essential for its function, facilitating the cis or trans dephosphorylation by increasing the local effective substrate concentration at both Cdc14 active sites and the dephosphorylation of sites both upstream and downstream of the PxL motif. The Cdc14-inhibitory Net1 protein not only occludes the Cdc14 active site but it also contacts the phosphatase at its non-catalytic domain A where its binding site overlaps with the PxL docking site, acting as a pseudosubstrate inhibitor (Kataria,2018).