Crystal structure of the human protein kinase CK2 regulatory subunit reveals its zinc finger-mediated dimerization

Protein kinase CK2 is a tetramer composed of two alpha catalytic subunits a nd two beta regulatory subunits, The structure of a C-terminal truncated fo rm of the human beta subunit has been determined by X-ray crystallography t o 1.7 Angstrom resolution. One dimer is observed in the asymmetric unit of the crystal. The most striking feature of the structure is the presence of a zinc finger mediating the dimerization. The monomer structure consists of two domains, one entirely alpha-helical and one including the zinc finger. The dimer has a crescent shape holding a highly acidic region at both ends . We propose that this acidic region is involved in the interactions with t he polyamines and/or catalytic subunits. Interestingly, conserved amino aci d residues among beta subunit sequences are clustered along one linear ridg e that wraps around the entire dimer, This feature suggests that protein pa rtners may interact with the dimer through a stretch of residues in an exte nded conformation.