Implications for Chk1 Regulation: The 1.7 Å Crystal Structure of Human Cell Cycle Checkpoint Kinase Chk1

et al., 1998). In S. pombe, Chk1 is essential for cell cycle arrest following DNA damage (Walworth et al., 1993; Walworth and Bernards, 1996; Lindsay et al., 1998). A checkpoint role for Chk1 has also been uncovered in Xenopus (Kumagai et al., 1998), and in cells from individPing Chen,* Chun Luo,* Yali Deng, Kevin Ryan, James Register, Stephen Margosiak, Anna Tempczyk-Russell, Binh Nguyen, Pamela Myers, Karen Lundgren, Chen-Chen Kan, and Patrick M. O’Connor Agouron Pharmaceuticals, Inc. uals defective in ATM (Chen et al., 1999). In this latter case, overexpression of Chk1 rescued the G2 check3565 General Atomics Court San Diego, California 92121 point defect of this cancer-prone phenotype, an outcome consistent with a G2 delay induced by overexpression of Chk1 (Walworth et al., 1993; Chen et al., 1999). In yeast, Chk1 also phosphorylates Wee1 (O’Connell et Summary al., 1997) and Pds1 (Sanchez et al., 1999). In the case of Pds1, which regulates DNA damage–induced arrest in The checkpoint kinase Chk1 is an important mediator of cell cycle arrest following DNA damage. The 1.7 Å S. cerevisiae, Chk1-dependent phosphorylation of Pds1 correlates with Pds1 resistance to degradation (Sanchez resolution crystal structures of the human Chk1 kinase domain and its binary complex with an ATP analog et al., 1999). Taken together, these results point to an important role for the Chk1 in regulating cell cycle arrest has revealed an identical open kinase conformation. The secondary structure and side chain interactions following DNA damage. The human Chk1 is a nuclear protein of 476 amino stabilize the activation loop of Chk1 and enable kinase activity without phosphorylation of the catalytic doacids (Sanchez et al., 1997). It contains a highly conserved N-terminal kinase domain (residues 1–265), a main. Molecular modeling of the interaction of a Cdc25C peptide with Chk1 has uncovered several conflexible linker region, and a less conserved C-terminal region with undefined function. The crystal structure of served residues that are important for substrate selectivity. In addition, we found that the less conserved the human Chk1 kinase domain (residues 1–289) described here provides important insights into Chk1 reguC-terminal region negatively impacts Chk1 kinase activity. lation and substrate selectivity.