Atomic Structure of Dual-Specificity Phosphatase 26, a Novel p53 Phosphatase

Regulation of p53 phosphorylation is critical to control its stability and biological activity. Dual-specificity phosphatase 26 (DUSP26) is a brain phosphatase highly overexpressed in neuroblastoma, which has been implicated in dephosphorylating phospho-Ser20 and phospho-Ser37 in the p53 transactivation domain. In this paper, we report the 1.68 angstrom crystal structure of a catalytically inactive mutant (Cys152Ser) of DUSP26 lacking the first 60 N-terminal residues (Delta N60-C/S-DUSP26). This structure reveals the architecture of a dual-specificity phosphatase domain related in structure to Vaccinia virus VH1. DUSP26 adopts a closed conformation of the protein tyrosine phosphatase (PTP)-binding loop, which results in an unusually shallow active site pocket and buried catalytic cysteine. A water molecule trapped inside the PTP-binding loop makes close contacts both with main chain and with side chain atoms. The hydrodynamic radius (R-H) of Delta N60-C/S-DUSP26 measured from velocity sedimentation analysis (R-H similar to 22.7 angstrom) and gel filtration chromatography (R-H similar to 21.0 angstrom) is consistent with an similar to 18 kDa globular monomeric protein. Instead in crystal, Delta N60-C/S-DUSP26 is more elongated (R-H similar to 37.9 angstrom), likely because of the extended conformation of C-terminal helix alpha 9, which swings away from the phosphatase core to generate a highly basic surface. As in the case of phosphatase MKP-4, we propose that a substrate-induced conformational change, possibly involving rearrangement of helix alpha 9 with respect to the phosphatase core, allows DUSP26 to adopt a catalytically active conformation. The structural characterization of DUSP26 presented in this paper provides the first atomic insight into this disease-associated phosphatase.