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BRCA2 controls RAD51 recombinase during homologous DNA recombination (HDR) through eight evolutionarily conserved BRC repeats, which individually engage RAD51 via the motif Phe-x-x-Ala. Using structure-guided molecular design, templated on a monomeric thermostable chimera between human RAD51 and archaeal RadA, we identify CAM833, a 529 Da orthosteric inhibitor of RAD51:BRC with a K d of 366 nM. The quinoline of CAM833 occupies a hotspot, the Phe-binding pocket on RAD51 and the methyl of the substituted α-methylbenzyl group occupies the Ala-binding pocket. In cells, CAM833 diminishes formation of damage-induced RAD51 nuclear foci; inhibits RAD51 molecular clustering, suppressing extended RAD51 filament assembly; potentiates cytotoxicity by ionizing radiation, augmenting 4N cell-cycle arrest and apoptotic cell death and works with poly-ADP ribose polymerase (PARP)1 inhibitors to suppress growth in BRCA2-wildtype cells. Thus, chemical inhibition of the protein-protein interaction between BRCA2 and RAD51 disrupts HDR and potentiates DNA damage-induced cell death, with implications for cancer therapy., Competing Interests: Declaration of interests Venkitaraman, Pellegrini, Blundell et al., WO2004035621 - Use of crystal structure of human RAD51-BRCA2 repeat complex in screening for anti tumor agents., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Notch is a receptor that mediates intercellular signaling through a pathway conserved across the metazoa. It is involved in cell fate assignation and pattern formation during development. The receptor acts as a membrane-tethered transcription factor and is activated by members of the Delta, Serrate, Lag-2 family of Notch ligands, which trigger two successive proteolytic cleavages of the receptor. The second cleavage releases the intracellular domain of Notch, which translocates to the nucleus, where it interacts with the CSL family of transcriptional regulators and forms part of a Notch target gene-activating complex. In the absence of signaling, CSL [CBF1, Su(H), Lag-1] regulators repress Notch target genes through interactions with several transcriptional co-repressors that recruit histone deacetylases and other chromatin-modifying enzymes. After forming, the transcription-activating binary Notch intracellular domain-CSL complex recruits several proteins that facilitate transcription, among them the coactivator MAM and histone acetylases. Transcription of target genes is terminated when the Notch intracellular domain is degraded in a proteasome-dependent manner.

Members of the Notch family of receptors act as membrane-tethered transcription factors that are tightly associated with binary cell fate decisions. Notch signaling acts as a molecular gate that allows cells to adopt or forfeit a particular fate. Interaction of Notch with ligands triggers a sequence of proteolytic cleavages that release the intracellular domain to the nucleus; this mechanism is a target of therapies for leukemias associated with Notch activation. Although the molecular mechanism of Notch activation is well characterized, further analysis in an appropriate cellular context will provide new insight into Notch signaling.

The salt BaSO(4) selectively adsorbs two proteins from crude Ornithodoros savignyi salivary gland extract. They co-purify during reversed-phase HPLC, but can be separated by hydrophobic-interaction chromatography. Their molecular masses are 9333 and 9173Da. The 9.3kDa protein was designated BSAP1 and the 9.1kDa protein BSAP2. Their amino acid compositions show significant differences, in particular the presence of seven and eight cysteine residues in BSAP1 and BSAP2, respectively. The proteins do not contain gamma-carboxyglutamic acid, hydroxyproline, or hydroxylysine. The proteins do not inhibit the intrinsic coagulation cascade, but inhibit the extrinsic pathway. The observed inhibition is not due to inhibition of factor VII. Both proteins bind to membranes. BSAP1 binds neutral and negatively charged membranes more strongly than BSAP2. Its affinity for negative membranes is, however, much lower than for neutral membranes. In contrast, BSAP2 binds both membranes equally strongly. The binding of the proteins to the membranes was significantly lowered upon pre-incubation with Ca(2+).