The 1κb kinase complex: random, sequential kinetics and activation by the c-terminal domain of iκbα
The multisubunit 1KB kinase (IKK) catalyzes the signal-inducible phosphorylation of N-terminal serines of iKBct, a key step in the activation of gene transcription by NF-xB. We demonstrate that binding of GSTiKBa and ATP to IKK occurs in a cooperative fashion, and that the mechanism for binding of these substrates is sequential. We show that peptides corresponding to the N-terminal and C-terminal phosphorylation domains of IKBa inhibit the IKK-catalyzed phosphorylation of OST-lKBa, and that the C-terminal peptide is a more effective inhibitor. In support of a sequential binding mechanism for substrates, inhibition by the C-terminal peptide is competitive with respect to GST-IicBa and mixed with respect to ATP. We demonstrate that both peptides are substrates for IKK, and that the N-terminal peptide competitively inhibits the IKK-catalyzed phosphorylation of the C-terminal peptide. We also observe that the presence of the C-terminal peptide enhances the rate of phosphorylation of the N-terminal peptide. This is consistent with an allosteric site present within IKK which recognizes the C-terminus of IKBa and activates the enzyme. This interaction with the C-terminus may represent an important mechanism by which the enzyme recognizes and phosphorylates iKBct.
Milled, KR; Burke, JR; Wood, MK; Meyers, CA
Volume / Issue
International Standard Serial Number (ISSN)