title: Regulatory motifs in Chk1.
abstract: Chk1 is the effector kinase of the G 2 DNA damage checkpoint. Chk1 homologs possess a highly conserved N-terminal kinase domain and a less conserved C-terminal regulatory domain. In response to DNA damage, Chk1 is recruited to mediator proteins assembled at lesions on replication protein A (RPA)-coated single-stranded DNA (ssDNA). Chk1 is then activated by phosphorylation on S345 in the C-terminal regulatory domain by the PI3 kinase-related kinases ATM and ATR to enforce a G 2 cell cycle arrest to allow time for DNA repair. Models have emerged in which this C-terminal phosphorylation relieves auto-inhibitory regulation of the kinase domain by the regulatory domain. However, experiments in fission yeast have shown that deletion of this putative auto-inhibitory domain actually inactivates Chk1 function. We show here that Chk1 homologs possess a kinase-associated 1 (KA1) domain that possesses residues previously implicated in Chk1 auto-inhibition. In addition, all Chk1 homologs have a small and highly conserved C-terminal extension (CTE domain). In fission yeast, both of these motifs are essential for Chk1 activation through interaction with the mediator protein Crb2, the homolog of human 53BP1. Thus, through different intra- and intermolecular interactions, these motifs explain why the regulatory domain exerts both positive and negative control over Chk1 activation. Such motifs may provide alternative targets to the ATP-binding pocket on which to dock Chk1 inhibitors as anticancer therapeutics.
authors: Department of Oncological Sciences, Mount Sinai School of Medicine, New York, NY, USA.
authors: Michael L
authors: ML
authors: Caparelli
authors: Matthew J
authors: MJ
authors: O'Connell
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000378:metabolism*; D000071877:Checkpoint Kinase 1; D004249:DNA Damage; D004260:DNA Repair; D004789:Enzyme Activation; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D054730:Protein Interaction Domains and Motifs; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051716:Replication Protein A / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000235:genetics / Q000378:metabolism*; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D018797:Cell Cycle Proteins; C109867:Crb2 protein, S pombe; D009687:Nuclear Proteins; D051716:Replication Protein A; D029702:Schizosaccharomyces pombe Proteins; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605873:Chk1 protein, S pombe
keywords: Chk1; DNA damage; KA1 domain; checkpoint; protein kinase