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Complex structure of human protein kinase CK2 catalytic subunit crystallized in the presence of a bisubstrate inhibitor
Structural highlights
FunctionCSK21_HUMAN Catalytic subunit of a constitutively active serine/threonine-protein kinase complex that phosphorylates a large number of substrates containing acidic residues C-terminal to the phosphorylated serine or threonine. Regulates numerous cellular processes, such as cell cycle progression, apoptosis and transcription, as well as viral infection. May act as a regulatory node which integrates and coordinates numerous signals leading to an appropriate cellular response. During mitosis, functions as a component of the p53/TP53-dependent spindle assembly checkpoint (SAC) that maintains cyclin-B-CDK1 activity and G2 arrest in response to spindle damage. Also required for p53/TP53-mediated apoptosis, phosphorylating 'Ser-392' of p53/TP53 following UV irradiation. Can also negatively regulate apoptosis. Phosphorylates the caspases CASP9 and CASP2 and the apoptotic regulator NOL3. Phosphorylation protects CASP9 from cleavage and activation by CASP8, and inhibits the dimerization of CASP2 and activation of CASP8. Regulates transcription by direct phosphorylation of RNA polymerases I, II, III and IV. Also phosphorylates and regulates numerous transcription factors including NF-kappa-B, STAT1, CREB1, IRF1, IRF2, ATF1, SRF, MAX, JUN, FOS, MYC and MYB. Phosphorylates Hsp90 and its co-chaperones FKBP4 and CDC37, which is essential for chaperone function. Regulates Wnt signaling by phosphorylating CTNNB1 and the transcription factor LEF1. Acts as an ectokinase that phosphorylates several extracellular proteins. During viral infection, phosphorylates various proteins involved in the viral life cycles of EBV, HSV, HBV, HCV, HIV, CMV and HPV.[1] [2] [3] [4] Publication Abstract from PubMedUp-regulation of an acidophilic protein kinase, CK2, has been established in several types of cancer. This cognition has made CK2 an important target for drug development for cancer chemotherapy. The characterization of potential drug candidates, determination of the structure and clarification of the functions of CK2 could be facilitated by the application of small-molecule fluorescent probes that bind to the active site of the enzyme with high affinity and selectivity. We have used a bisubstrate approach for the development of a highly potent inhibitor of CK2. 4,5,6,7-Tetrabromo-1H-benzimidazole was conjugated with peptides containing multiple aspartate residues via different linkers. The design of the inhibitors was by crystallographic analysis of the complex of an inhibitor with the catalytic subunit of the enzyme (CK2alpha). The inhibitory potency of the synthesized compounds was established in a kinetic assay that used thin layer chromatography for the measurement of the rate of phosphorylation of fluorescently labelled peptide 5-TAMRA-RADDSDDDDD. The most potent inhibitor, ARC-1502 (K(i) = 0.5 nM), revealed high selectivity for CK2alpha in a panel of 140 protein kinases. Labelling of ARC-1502 with PromoFluor-647 gave the fluorescent probe ARC-1504 that possessed subnanomolar affinity towards both CK2alpha and the holoenzyme. The probe was used in a fluorescence anisotropy-based binding assay to measure the concentration of CK2alpha and characterize non-labelled ligands binding to the active site of CK2alpha. A subnanomolar fluorescent probe for protein kinase CK2 interaction studies.,Enkvist E, Viht K, Bischoff N, Vahter J, Saaver S, Raidaru G, Issinger OG, Niefind K, Uri A Org Biomol Chem. 2012 Oct 2. PMID:23032938[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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