Protein kinase CK2 is a ubiquitous kinase that can phosphorylate hundreds of cellular proteins and plays important roles in cell growth and development. Deregulation of CK2 is related to a variety of human cancers, and CK2 is regarded as a suppressor of apoptosis; therefore, it is a target of anticancer therapy. Nucleolar phosphoprotein 140 (Nopp140), which is an intrinsically disordered protein, interacts with CK2 and inhibits the latter's catalytic activity in vitro. Interestingly, the catalytic activity of CK2 is recovered in the presence of D-myo-inositol 1,2,3,4,5,6-hexakisphosphate (IP 6 ). IP 6 is widely distributed in animal cells, but the molecular mechanisms that govern its cellular functions in animal cells have not been completely elucidated. In this study, the crystal structure of CK2 in complex with IP 6 showed that the lysine-rich cluster of CK2 plays an important role in binding to IP 6 . The biochemical experiments revealed that a Nopp140 fragment (residues 568-596) and IP 6 competitively bind to the catalytic subunit of CK2 (CK2α), and phospho-Ser574 of Nopp140 significantly enhances its interaction with CK2α. Substitutions of K74E, K76E, and K77E in CK2α significantly reduced the interactions of CK2α with both IP 6 and the Nopp140-derived peptide. Our study gives an insight into the regulation of CK2. In particular, our work suggests that CK2 activity is inhibited by Nopp140 and reactivated by IP 6 by competitive binding at the substrate recognition site of CK2.inositol hexakisphosphate | IDP | phosphorylation P rotein phosphorylation is a major aspect of signaling in cells including cell cycle (1). Casein kinase 2 (CK2) is a ubiquitous protein kinase that is essential for cell growth (2), development, and other essential cellular processes (3-7). More than 300 proteins that are involved in DNA replication, transcription, translation, and signal transduction are phosphorylated by CK2 (8). CK2 is also involved in the regulation of apoptosis (9, 10). CK2-dependent phosphorylation of AKT kinase, which is essential for cell survival, activates cells to resist apoptosis (11,12). In addition, CK2-dependent phosphorylation of β-catenin, which induces cell proliferation by Wnt signaling, increases its stability and ability to resist proteolysis (13). Deregulation of CK2 is strongly related to a variety of human cancers (14-17), and therefore, CK2 is considered a target for anticancer therapy (18).Structural and biochemical studies have revealed the molecular architecture and catalytic mechanism of CK2. CK2 consists of two catalytic subunits (α and α′) and two regulatory subunits (β) which can form α 2 β 2 or αα′β 2 heterotetramers (19). The crystal structure of the CK2 holoenzyme is composed of a central dimer of regulatory subunits with catalytic subunits bound to them (20). The active site and residues that are critical for substrate binding have been identified (21). The structure of CK2α in complex with an ATP-analog inhibitor showed a common ATP binding pocket that consists of the residues Lys68,...

As anti-HCV aryl diketoacids (ADK) are good metal chelators, we anticipated that ADKs might serve as potential inhibitors of SARS CoV (SCV) NTPase/helicase (Hel) by mimicking the binding modes of the bismuth complexes which effectively competes for the Zn(2+) ion binding sites in SCV Hel thereby disrupting and inhibiting both the NTPase and helicase activities. Phosphate release assay and FRET-based assay of the ADK analogues showed that the ADKs selectively inhibit the duplex DNA-unwinding activity without significant impact on the helicase ATPase activity. Also, antiviral activities of the ADKs were shown dependent upon the substituent. Taken together, these results suggest that there might be ADK-specific binding site in the SCV Hel, which warrants further investigations with diverse ADKs to provide valuable insights into rational design of specific SCV Hel inhibitors.

Fusion between the envelope of HIV and the plasma membrane of target cells is mediated by gp41, the envelope glycoprotein of HIV. Peptides derived from the membrane-proximal helical motif of the extracellular domain of gp41 effectively inhibit the infection of HIV, and their inhibitory activities are known to be correlated with the helical propensity of the peptides. We have designed small peptides that can form a stable alpha helix and thereby inhibit gp120/41-mediated cell fusion. A 19-mer peptide from the membrane-proximal helical motif of gp41 had no secondary structure in solution, and failed to block gp41-mediated cell fusion. When amino acids with low helical propensity were substituted, and helix-capping sequences were introduced at both ends of the peptides, the modified peptides formed a stable helical structure. They also bound to the coiled-coil motif of gp41 presented at the C terminus of thioredoxin and blocked the cell fusion mediated by gp120/41. These results implied that such modification was enough to change a short peptide derived from gp41 into a potent inhibitor against the infection of HIV.

Biomolecules specific to explosives can be exploited as chemical sensors. Peptides specific to immobilized dinitrotoluene (DNT) were identified using a phage display library. A derivative of DNT that contained an extended amine group, 4-(2,4-dinitrophenyl)butan-1-amine, was synthesized and immobilized using a self-assembled monolayer surface on gold. Filamentous M13 phages displaying random sequences of 12-mer peptides specific to the immobilized DNTderivate were isolated from the M13 phage library by biopanning. A common peptide sequence was identified from the isolated phages and the synthesized peptides showed selective binding to DNT. When the peptide was immobilized on a quartz crystal microbalance (QCM) chip, it showed a binding signal to DNT, while toluene barely showed significant binding to the QCM chip. These results demonstrate that peptides screened by biopanning against immobilized DNT can be useful for quick and accurate detection of DNT.

Bacterial UDP-N-acetylglucosamine enolpyruvyl transferase (MurA) catalyzes the transfer of enolpyruvate from phosphoenolpyruvate (PEP) to uridine diphospho-Nacetylglucosamine (UNAG), which is the first step of bacterial cell wall synthesis. We identified thimerosal, thiram, and ebselen as effective inhibitors of Haemophilus influenzae MurA by screening a chemical library that consisted of a wide range of bioactive compounds. When MurA was preincubated with these inhibitors, their 50% inhibitory concentrations (IC 50 s) were found to range from 0.1 to 0.7 µM. In particular, thimerosal suppressed the growth of several different Gram-negative bacteria such as Escherichia coli, Pseudomonas aeruginosa, and Salmonella typhimurium at a concentration range of 1-2 µg/ml. These inhibitors covalently modified the cysteine residue near the active site of MurA. This modification changed the open conformation of MurA to a more closed configuration, which may have prevented the necessary conformational change from occurring during the enzyme reaction.