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,...

DNA-binding repressors are involved in transcriptional repression in many organisms. Disabling a repressor is a crucial step in activating expression of desired genes. Thus, several mechanisms have been identified for the removal of a stably bound repressor (Rep) from the operator. Here, we describe an uncharacterized mechanism of noncanonical DNA binding and induction by a Rep from the temperate Salmonella phage SPC32H; this mechanism was revealed using the crystal structures of homotetrameric Rep (92–198) and a hetero-octameric complex between the Rep and its antirepressor (Ant). The canonical method of inactivating a repressor is through the competitive binding of the antirepressor to the operator-binding site of the repressor; however, these studies revealed several noncanonical features. First, Ant does not compete for the DNA-binding region of Rep. Instead, the tetrameric Ant binds to the C-terminal domains of two asymmetric Rep dimers. Simultaneously, Ant facilitates the binding of the Rep N-terminal domains to Ant, resulting in the release of two Rep dimers from the bound DNA. Second, the dimer pairs of the N-terminal DNA-binding domains originate from different dimers of a Rep tetramer (trans model). This situation is different from that of other canonical Reps, in which two N-terminal DNA-binding domains from the same dimeric unit form a dimer upon DNA binding (cis model). On the basis of these observations, we propose a noncanonical model for the reversible inactivation of a Rep by an Ant.

CO2 fixation is thought to be one of the key factors in mitigating global warming. Of the various methods for removing CO2, the NAD-dependent formate dehydrogenase from Candida boidinii (CbFDH) has been widely used in various biological CO2-reduction systems; however, practical applications of CbFDH have often been impeded owing to its low CO2-reducing activity. It has recently been demonstrated that the NAD-dependent formate dehydrogenase from Thiobacillus sp. KNK65MA (TsFDH) has a higher CO2-reducing activity compared with CbFDH. The crystal structure of TsFDH revealed that the biological unit in the asymmetric unit has two conformations, i.e. open (NAD(+)-unbound) and closed (NAD(+)-bound) forms. Three major differences are observed in the crystal structures of TsFDH and CbFDH. Firstly, hole 2 in TsFDH is blocked by helix α20, whereas it is not blocked in CbFDH. Secondly, the sizes of holes 1 and 2 are larger in TsFDH than in CbFDH. Thirdly, Lys287 in TsFDH, which is crucial for the capture of formate and its subsequent delivery to the active site, is an alanine in CbFDH. A computational simulation suggested that the higher CO2-reducing activity of TsFDH is owing to its lower free-energy barrier to CO2 reduction than in CbFDH.

No abstract

No abstract