Specific characteristics of CK2β regulatory subunits in plants.

In all eukaryotes, the typical CK2 holoenzyme is an heterotetramer composed of two catalytic (CK2α and CK2α') and two regulatory (CK2β) subunits. One of the distinctive traits of plant CK2 is that they present a greater number of genes encoding for CK2α/β subunits than animals or yeasts, for instance, in Arabidopsis and maize both CK2α/β subunits belong to multigenic families composed by up to four genes. Here, we conducted a genome-wide survey examining 34 different plant genomes in order to investigate if the multigenic property of CK2β genes is a common feature through the entire plant kingdom. Also, at the level of structure, the plant CK2β regulatory subunits present distinctive features as (i) they lack about 20 aminoacids in the C-terminal domain, (ii) they present a specific N-terminal extension of about 90 aminoacids that shares no homology with any previously characterized functional domain, and (iii) the acidic loop region is poorly conserved at the aminoacid level. Since there is no data about CK2β or holoenzyme structure in plants, in this study, we use human CK2β as a template to predict a structure for Zea mays CK2β1 by homology modeling and we discuss about possible structural changes in the acidic loop region that could affect the enzyme regulation.