The C-terminal domain of human grp94 protects the catalytic subunit of protein kinase CK2 (CK2 alpha) against thermal aggregation - Role of disulfidebonds

The C-terminal domain (residues 518-803) of the 94 kDa glucose regulated pr otein (grp94) was expressed in Escherichia coli as a fusion protein with a His(6)-N-terminal tag (grp94-CT). This truncated form of grp94 formed dimer s and oligomers that could be dissociated into monomers by treatment with d ithiothreitol. Grp94-CT conferred protection against aggregation on the cat alytic subunit of protein kinase CK2 (CK2 alpha), although it did not prote ct against thermal inactivation. This anti-aggregation effect of grp94-CT w as concentration dependent, with full protection achieved at grp94-CT/CK2 a lpha molar ratios of 4 : 1. The presence of dithiothreitol markedly reduced the anti-aggregation effects of grp94-CT on CK2 alpha without altering the solubility of the chaperone. It is concluded that the chaperone activity o f the C-terminal domain of human grp94 requires the maintenance of its quat ernary structure (dimers and oligomers), which seems to be stabilised by di sulphide bonds.