The carboxy-terminal domain of Grp94 binds to protein kinase CK2 alpha but not to CK2 holoenzyme.

Surface plasmon resonance analysis shows that the carboxy-terminal domain of Grp94 (Grp94-CT, residues 518-803) physically interacts with the catalytic subunit of protein kinase CK2 (CK2 alpha) under non-stressed conditions. A K(D) of 4 x 10(-7) was determined for this binding. Heparin competed with Grp94-CT for binding to CK2 alpha. CK2 beta also inhibited the binding of Grp94-CT to CK2 alpha, and CK2 holoenzyme reconstituted in vitro was unable to bind Grp94-CT. The use of CK2 alpha mutants made it possible to map the Grp94-CT binding site to the four lysine stretch (residues 74-77) present in helix C of CK2 alpha. Grp94-CT stimulated the activity of CK2 alpha wild-type but was ineffective on the CK2 alpha K74-77A mutant.