Quaternary structure of casein kinase 2. Characterization of multiple oligomeric states and relation with its catalytic activity.
The structure-activity relationship of casein kinase 2 (CK2) was examined with regard to its previously reported property to self-aggregate in vitro. Sedimentation velocity and electron microscopy studies showed that the purified kinase exhibited four major, different oligomeric forms in aqueous solution. This self-polymerization was a reproducible and fully reversible process, highly dependent upon the ionic strength of the medium, suggesting that electrostatic interactions are mostly involved. At high salt concentrations (e.g. 0.5 M NaCl), CK2 appears as spherical moieties with a 18.7 +/- 1.6 nm average diameter, roughly corresponding to the alpha 2 beta 2 protomer, as deduced by measurements of the Stokes radius and by light scattering studies. At lower ionic strength (e.g. 0.2 M NaCl), the protomers associate to form ring-like structures with a diameter (averaging 36.6 +/- 2.1 nm) and Stokes radius indicating that they are most likely made of four circularly associated alpha 2 beta 2 protomers. At 0.1 M NaCl, two additional polymeric structures were visualized: thin filaments (16.4 +/- 1.4 nm average), as long as 1 to 5 microns, and thick and shorter filaments (28.5 +/- 1.6 nm average). Examination of the molecular organization of CK2 under different catalytic conditions revealed that the ring-like structure is the favored conformation adopted by the enzyme in the presence of saturating concentrations of substrates and cofactors. During catalysis, well-known cofactors like MgCl2 or spermine are the main factors governing the stabilization of the active ring-like structure. On the other hand, inhibitory high salt concentrations promote the dissociation of the active ring-like structure into protomers. Such observations suggest a strong correlation between the ring-like conformation of the enzyme and optimal specific activity. Thus, CK2 may be considered as an associating-dissociating enzyme, and this remarkable property supports the hypothesis of a cooperative and allosteric regulation of the kinase in response to appropriate regulatory ligands possibly taking place in intact cells.
Valero
E
E
Commissariat á l'Energie Atomique, Biochimie des Régulations Cellulaires Endocrines, INSERM Unit 244, Département de Biologie Moléculaire et Structurale, CEN.G, Grenoble, France.
De Bonis
S
S
Filhol
O
O
Wade
R H
RH
Langowski
J
J
Chambaz
E M
EM
Cochet
C
C
D000595:Amino Acid Sequence; D000818:Animals; D001704:Biopolymers; D047390:Casein Kinase II; D002384:Catalysis; D003001:Cloning, Molecular; D004331:Drosophila melanogaster; D015636:Magnesium Chloride / Q000494:pharmacology; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D011487:Protein Conformation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D012965:Sodium Chloride; D012996:Solutions; D013096:Spermine / Q000494:pharmacology; D013329:Structure-Activity Relationship; D014867:Water
D001704:Biopolymers; D012996:Solutions; D015636:Magnesium Chloride; D014867:Water; D013096:Spermine; D012965:Sodium Chloride; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases