Characterization of the InsP6-dependent interaction between CK2 and Nopp140

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Nopp140 is a nucleolar protein that negatively regulates Casein Kinase 2 (CK2).
• CK2 is a critical kinase involved in cell proliferation.
• Understanding the interaction between Nopp140 and CK2 is crucial for cell cycle regulation.

Purpose of the Study:

• To quantitatively analyze the interaction between CK2 subunits and Nopp140.
• To characterize the inhibitory mechanism of inositol hexaphosphate (InsP(6)) on this interaction.
• To elucidate how InsP(6) affects Nopp140-mediated regulation of CK2 activity.

Main Methods:

• Yeast two-hybrid assays to identify binding regions.
• Direct measurement of protein-protein interactions.
• Quantitative analysis of enzyme kinetics and inhibition constants (K(d), IC(50)).

Main Results:

• Nopp140 specifically binds to the catalytic subunit CK2alpha with a dissociation constant (K(d)) of 4 nM.
• The C-terminal region of Nopp140 mediates binding to CK2alpha.
• InsP(6) binds to CK2alpha and inhibits the Nopp140-CK2alpha interaction with an IC(50) of 25 microM, attenuating Nopp140's repression of CK2 activity.

Conclusions:

• Nopp140 directly inhibits CK2 catalytic activity through specific binding to CK2alpha.
• InsP(6) acts as an allosteric inhibitor, disrupting the Nopp140-CK2alpha complex.
• This mechanism reveals a novel regulatory pathway for CK2 activity and cell proliferation.