Notch receptors transmit signals between adjacent cells. Signaling is initiated when ligand binding induces metalloprotease cleavage of Notch within an extracellular negative regulatory region (NRR). We present here the X-ray structure of the human NOTCH2 NRR, which adopts an autoinhibited conformation. Extensive interdomain interactions within the NRR bury the metalloprotease site, showing that a substantial conformational movement is necessary to expose this site during activation by ligand. Leukemia-associated mutations in NOTCH1 probably release autoinhibition by destabilizing the conserved hydrophobic core of the NRR.
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We thank Mike Eck and Angela Toms for crystallographic suggestions and Kelly Arnett and Mike Malecki for critical reading of the manuscript. This work was supported by American Cancer Society Postdoctoral Fellowships (WRG and DVU), a Leukemia and Lymphoma Society Fellowship (WRG), and NIH grants to SCB and JCA.