Intermolecular contact sites in protein kinase CK2.

Chemical crosslinking and analysis of CNBr-digested fusion products by immunoblotting with sequence-specific antibodies identifies an interaction between positions 55-70 of subunit beta (beta55-70) and 65-80 of subunit alpha (alpha65-80). This has been supported by crosslinking of subunits with peptides alpha65-80 and beta55-70, by binding of subunits to immobilized peptides, and by the hindrance of coprecipitation with peptide-raised antibodies (anti-alpha65-80; anti-beta55-70). Functionally, beta55-70 is a negative regulatory region for the kinase activity of subunit alpha. The opposite, stimulatory property of subunit beta has been assigned to its C-terminal part. Subdivision of peptide beta155-181, that has stimulatory effect, into overlapping peptides and assaying for alpha binding and binding competition revealed a tight physical contact at beta162-175. This region, however, is non-stimulatory indicating binding a necessary but not sufficient quality for stimulation. A contact might exist to regions surrounding C147 and/or C220 at subunit alpha as indicated by crosslinking and peptide competition. The crosslinking data also confirm a beta-beta contact in CK2 holoenzyme. Effects by non-ionic detergents show hydrophobic interactions to play an important role in catalytic activity adjustment.