Crystal structure of the catalytic subunit of Cdc25B required for G(2)/M phase transition of the cell cycle

Cdc25B is a dual specificity phosphatase involved in the control of cyclin- dependent kinases and the progression of cells through the cell cycle. A se ries of minimal domain Cdc25B constructs maintaining catalytic activity hav e been expressed. The structure of a minimum domain construct binding sulfa te was determined at 1.9 Angstrom resolution and a temperature of 100 K. Ot her forms of the same co?nstruct were determined at lower resolution and ro om temperature. The overall folding and structure of the domain is Similar to that found for Cdc25A. An important difference between the two is that t he Cdc25B domain binds oxyanions in the catalytic site while that of Cdc25A appears unable to bind oxyanions. There are also important conformational differences in the C-terminal region. Ln Cdc25B, both sulfate and tungstate anions are shown to bind in the catalytic site containing the signature mo tif (HCxxxxxR) in a conformation similar to that of other protein tyrosine phosphatases and dual specificity phosphatases, with the exception of the C dc25A. The Cdc25B constructs, with various truncations of the C-terminal re sidues, are shown to have potent catalytic activity. When cut back to the s ite at which the Cdc25A structure begins to deviate from the Cdc25B structu re, the activity is considerably less. There is a pocket extending from the catalytic site to an anion-binding site containing a chloride about 14 Ang strom away. The catalytic cysteine residue, Cys473, can be oxidized to form a disulfide linkage to Cys426. A readily modifiable cysteine residue, Cys4 84, resides in another pocket that binds a sulfate but not in the signature motif conformation. This region of the structure is highly conserved betwe en the Cdc25 molecules and could serve some unknown function. (C) 1999 Acad emic Press.