Drosophila cryptochrome (dCRY) is a FAD-dependent circadian photoreceptor, whereas mammalian cryptochromes (CRY1/2) are integral clock components that repress mCLOCK/mBMAL1-dependent transcription. We report crystal structures of full-length dCRY, a dCRY loop deletion construct, and the photolyase homology region of mouse CRY1 (mCRY1). Our dCRY structures depict Phe534 of the regulatory tail in the same location as the photolesion in DNA-repairing photolyases and reveal that the sulfur loop and tail residue Cys523 plays key roles in the dCRY photoreaction. Our mCRY1 structure visualizes previously characterized mutations, an NLS, and MAPK and AMPK phosphorylation sites. We show that the FAD and antenna chromophore-binding regions, a predicted coiled-coil helix, the C-terminal lid, and charged surfaces are involved in FAD-independent mPER2 and FBXL3 binding and mCLOCK/mBMAL1 transcriptional repression. The structure of a mammalian cryptochrome1 protein may catalyze the development of CRY chemical probes and the design of therapeutic metabolic modulators.

Intensive anticancer drug discovery efforts have been made to develop small molecule inhibitors of the p53-MDM2 and p53-MDMX interactions. We present here the structures of the most potent inhibitors bound to MDM2 and MDMX that are based on the new imidazo-indole scaffold. In addition, the structure of the recently reported spiro-oxindole inhibitor bound to MDM2 is described. The structures indicate how the substituents of a small molecule that bind to the three subpockets of the MDM2/X-p53 interaction should be optimized for effective binding to MDM2 and/or MDMX. While the spiro-oxindole inhibitor triggers significant ligand-induced changes in MDM2, the imidazo-indoles share similar binding modes for MDMX and MDM2, but cause only minimal induced-fit changes in the structures of both proteins. Our study includes the first structure of the complex between MDMX and a small molecule and should aid in developing efficient scaffolds for binding to MDMX and/or MDM2.

No abstract