Role of plant-specific N-terminal domain of maize CK2?1 subunit in CK2? 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 (CK2?) and the regulatory (CK2?). The CK2? subunits enhance the stability, activity and specificity of the holoenzyme, but they can also perform functions independently of the CK2 tetramer. CK2? 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 CK2? subunit sequences reveals its arrangement through short, conserved motifs, some of them including CK2 autophosphorylation sites. By using maize CK2?1 and a deleted version (?NCK2?1) lacking the N-terminal domain, we have demonstrated that CK2?1 is autophosphorylated within the N-terminal domain. Moreover, the holoenzyme composed with CK2?1/?NCK2?1 is able to phosphorylate different substrates more efficiently than CK2?1/CK2?1 or CK2? alone. Transient overexpression of CK2?1 and ?NCK2?1 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 CK2?/? subunits mainly observed in the nucleus. All together, our results support the hypothesis that the plant-specific N-terminal domain of CK2? subunits is involved in the down-regulation of the CK2 holoenzyme activity and in the stabilization of CK2?1 protein. In summary, the whole amount of data shown in this work suggests that this domain was acquired by plants for regulatory purposes.

SUBMITTER: Riera M 

PROVIDER: S-EPMC3137599 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature