The Chk2 Ser/Thr kinase plays crucial, evolutionarily conserved roles in cellular responses to DNA damage. Identification of two pro-oncogenic mutations within the Chk2 FHA domain has highlighted its importance for Chk2 function in checkpoint activation. The X-ray structure of the Chk2 FHA domain in complex with an in vitro selected phosphopeptide motif reveals the determinants of binding specificity and shows that both mutations are remote from the peptide binding site. We show that the Chk2 FHA domain mediates ATM-dependent Chk2 phosphorylation and targeting of Chk2 to in vivo binding partners such as BRCA1 through either or both of two structurally distinct mechanisms. Although phospho-dependent binding is important for Chk2 activity, previously uncharacterized phospho-independent FHA domain interactions appear to be the primary target of oncogenic lesions.
Bibliographical noteFunding Information:
We thank Will Mawby (University of Bristol) for synthesis of native and selenomethionine-containing phosphopeptides; James Nicholson and Elizabeth Duke for beamline assistance at the SRS, Daresbury; Gordon Leonard for beamline assistance at ESRF, Grenoble; and Graeme Smith for providing the Chk2 cDNA clone. We gratefully acknowledge the help of S.J. Gamblin with crystal handling and Steve Gamblin and Katrin Rittinger for critical reading of the manuscript. B.W. was supported by grants from the Association for International Cancer Research and the Human Frontiers Science Programme. The S.P.J. laboratory is funded by grants from Cancer Research UK, the Association for International Cancer Research, and the A-T Medical Research Trust. The M.B.Y. laboratory is funded by grant GM60594 from the NIH.