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Abstract

Protein kinase CK2 is characterized by a number of features, including substrate specificity, inhibition by polyanionic compounds and intrasteric down-regulation by its beta-subunit, which denote a special aptitude to interact with negatively charged ligands. This situation may reflect the presence in CK2 catalytic subunits of several basic residues that are not conserved in the majority of other protein kinases. Some of these residues, notably K49 in the 'Gly rich loop', K74, K75, K76, K77, K79, R80, K83 in the 'Lys rich segment' and R191, R195, K198 in the 'p+1 loop', have been shown by mutational studies to be implicated to various extents and with distinct roles in substrate recognition, inhibition by heparin and by pseudosubstrate and instrasteric regulation. Molecular modelization based on crystallographic data provide a rationale for the biochemical observations, showing that several of these basic residues are clustered around the active site where they make contact with individual acidic residues of the peptide substrate. They can also mediate the effect of polyanionic inhibitors (e.g. heparin) and of regulatory elements present in the beta-subunit, in the N terminal segment of the catalytic subunit and possibly in other proteins interacting with CK2. Our data also disclose a unique mode of binding of the phosphoacceptor substrate which bridges across the catalytic cleft making contacts with both the lower and upper lobes of CK2.

The Protein Kinase CK2 Phosphorylates SNAP190 to Negatively Regulate SNAPC DNA Binding and Human U6 Transcription by RNA Polymerase III

“…The increased negative charge density is predicted to facilitate interactions with the positively charged arginine-rich region located adjacently to the SNAP190 Myb DNA binding domain and interfere with DNA contacts by the recognition helices within the SNAP190 Rc and Rd Myb repeats. In support of this model, alanine substitution of the SNAP190 EED sequence, which does not contribute to direct DNA contacts, but instead likely comprises an important component of the acidophilic CK2 recognition motifs (30,31), reduced SNAP190 phosphorylation and prevented CK2 inhibition of DNA binding by SNAP C , without compromising DNA binding in the absence of CK2 phosphorylation.…”

Ordered Phosphorylation Events in Two Independent Cascades of the PTEN C-tail Revealed by NMR

“…Consensus and Predictions. These nine phosphorylation sites lie within a CK2 or GSK3β consensus motif [17][18][19]30 and could have been somehow predicted. For S361 and T363 sites possibly controlled by CK2, the acidic charges (represented by phosphorylated Ser/Thr) are less abundant between positions n − 1 to n + 4, which could justify their slower kinetics.…”

The Raison D'Être of Constitutively Active Protein Kinases: The Lesson of CK2

“…Why is CK2 so markedly acidophilic? A systematic mutational analysis − has led to the identification of a number of basic residues which are responsible for interactions with different acidic determinants within the optimal peptide substrate RRR-A-DDSDDDDD: these residues are conserved across CK2 catalytic subunits from different species, while they are replaced by non basic residues in the majority of other kinases. They belong to distinct structural elements, namely, a KKKK quartet (residues 74−77) at the beginning of helix-C (responsible for the interaction with the crucial determinant at position n + 3 and probably also with others down stream from it), to the n + 1 loop (K-198, interacting with the determinant at position n + 1), and to the Gly-rich loop where R47 and K49 interact with the acidic determinants at positions n − 1 and n + 2, whenever present.…”