title: Role of plant-specific N-terminal domain of maize CK2β1 subunit in CK2β functions and holoenzyme regulation.
abstract: Protein kinase CK2 is a highly pleiotropic Ser/Thr kinase ubiquituous in eukaryotic organisms. CK2 is organized as a heterotetrameric enzyme composed of two types of subunits: the catalytic (CK2α) and the regulatory (CK2β). The CK2β subunits enhance the stability, activity and specificity of the holoenzyme, but they can also perform functions independently of the CK2 tetramer. CK2β regulatory subunits in plants differ from their animal or yeast counterparts, since they present an additional specific N-terminal extension of about 90 aminoacids that shares no homology with any previously characterized functional domain. Sequence analysis of the N-terminal domain of land plant CK2β subunit sequences reveals its arrangement through short, conserved motifs, some of them including CK2 autophosphorylation sites. By using maize CK2β1 and a deleted version (ΔNCK2β1) lacking the N-terminal domain, we have demonstrated that CK2β1 is autophosphorylated within the N-terminal domain. Moreover, the holoenzyme composed with CK2α1/ΔNCK2β1 is able to phosphorylate different substrates more efficiently than CK2α1/CK2β1 or CK2α alone. Transient overexpression of CK2β1 and ΔNCK2β1 fused to GFP in different plant systems show that the presence of N-terminal domain enhances aggregation in nuclear speckles and stabilizes the protein against proteasome degradation. Finally, bimolecular fluorescence complementation (BiFC) assays show the nuclear and cytoplasmic location of the plant CK2 holoenzyme, in contrast to the individual CK2α/β subunits mainly observed in the nucleus. All together, our results support the hypothesis that the plant-specific N-terminal domain of CK2β subunits is involved in the down-regulation of the CK2 holoenzyme activity and in the stabilization of CK2β1 protein. In summary, the whole amount of data shown in this work suggests that this domain was acquired by plants for regulatory purposes.
authors.affiliation: Department of Molecular Genetics, Centre for Research on Agricultural Genomics CRAG, CSIC-IRTA-UAB, Barcelona, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Riera
authors.forename: Sami
authors.initials: S
authors.lastname: Irar
authors.forename: Isabel C
authors.initials: IC
authors.lastname: Vélez-Bermúdez
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Carretero-Paulet
authors.forename: Victoria
authors.initials: V
authors.lastname: Lumbreras
authors.forename: Montserrat
authors.initials: M
authors.lastname: Pagès
mesh_terms: D000595:Amino Acid Sequence; D047390:Casein Kinase II / Q000737:chemistry* / Q000378:metabolism*; D004795:Enzyme Stability; D019143:Evolution, Molecular; D020035:Holoenzymes / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D019441:Plant Epidermis / Q000166:cytology / Q000201:enzymology; D018515:Plant Leaves / Q000166:cytology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry* / Q000378:metabolism*; D021381:Protein Transport; D020539:Sequence Analysis, Protein; D013045:Species Specificity; D013329:Structure-Activity Relationship; D013347:Subcellular Fractions / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology; D003313:Zea mays / Q000201:enzymology*
chemical_list: D020035:Holoenzymes; D021122:Protein Subunits; D047390:Casein Kinase II; D046988:Proteasome Endopeptidase Complex