Biochemical and three-dimensional-structural study of the specific inhibition of protein kinase CK2 by [5-oxo-5,6-dihydroindolo-(1,2-a)quinazolin-7-yl]acetic acid (IQA)

Stefania Sarno, Erika de Moliner, Maria Ruzzene, Mario A. Pagano, Roberto Battistutta, Jenny Bain, Doriano Fabbro, Joseph Schoepfer, Matthew Elliott, Pascal Furet, Flavio Meggio, Giuseppe Zanotti, Lorenzo A. Pinna (Lead / Corresponding author)

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    134 Citations (Scopus)


    IQA [[5-oxo-5,6-dihydro-indolo(1,2-a)quinazolin-7-yl]acetic acid] is a novel ATP/GTP site-directed inhibitor of CK2 ('casein kinase 2'), a pleiotropic and constitutively active protein kinase whose activity is abnormally high in transformed cells. The Ki value of IQA (0.17 µM) is lower than those of other CK2 inhibitors reported so far. Tested at 10 µM concentration in the presence of 100 µM ATP, IQA almost suppresses CK2 activity in vitro, whereas it is ineffective or weakly effective on a panel of 44 protein kinases and on phosphoinositide 3-kinase. In comparison, other CK2 inhibitors, notably apigenin and quercetin, are more promiscuous. The in vivo efficacy of IQA has been assessed by using the fact that treatment of Jurkat cells with IQA inhibits endogenous CK2 in a dose-dependent manner. IQA has been co-crystallized with maize CK2α, which is >70% identical with its human homologue, and the structure of the complex has been determined at 1.68 Å (1 Å=0.1 nm) resolution. The inhibitor lies in the same plane occupied by the purine moiety of ATP with its more hydrophobic side facing the hinge region. Major contributions to the interaction are provided by hydrophobic forces and non-polar interactions involving the aromatic portion of the inhibitor and the hydrophobic residues surrounding the ATP-binding pocket, with special reference to the side chains of V53 (Val53), I66, M163 and I174. Consequently, mutants of human CK2α in which either V66 (the homologue of maize CK2α I66) or I174 is replaced by alanine are considerably less sensitive to IQA inhibition when compared with wild-type. These results provide new tools for deciphering the enigmatic role of CK2 in living cells and may pave the way for the development of drugs depending on CK2 activity.

    Original languageEnglish
    Pages (from-to)639-646
    Number of pages8
    JournalThe Biochemical journal
    Issue number3
    Publication statusPublished - 15 Sept 2003


    • Acetates/chemistry
    • Animals
    • Casein Kinase II
    • Cell Line
    • Crystallography, X-Ray
    • Enzyme Inhibitors/chemistry
    • Humans
    • Jurkat Cells
    • Molecular Structure
    • Plant Proteins/antagonists & inhibitors
    • Protein Structure, Quaternary/drug effects
    • Protein-Serine-Threonine Kinases/antagonists & inhibitors
    • Quinazolines/chemistry
    • Rats
    • Zea mays/enzymology


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