The Crystal Structure of the Active Form of the C-Terminal Kinase Domain of Mitogen- And Stress-Activated Protein Kinase 1

摘要

Mitogen- and stress-activated protein kinase 1 (MSK1) is a growth factor-stimulated serine/threonine kinase that is involved in gene transcription regulation and proinflammatory cytokine stimulation. MSK1 is a dual kinase possessing two non-identical protein kinase domains in one polypeptide. We present the active conformation of the crystal structures of its C-terminal kinase domain (CTD) in apo form and complexed with a non-hydrolyzable ATP analogue at 2.0 Å and 2.5 Å resolution, respectively. Structural analysis revealed substantial differences in the contacts formed by the C-terminal helix, which is responsible for the inactivity of other autoinhibited kinases. In CTD MSK1, the C-terminal αL-helix is located in the surface groove, but forms no hydrogen bonding with the substrate-binding loop or nearby helices, and does not interfere with the protein's autophosphorylation activity. Mutational analysis confirmed that the αL-helix is inherently non-autoinhibitory. Overexpression of the single C-terminal kinase domain in JB6 cells resulted in tumor promoter-induced neoplastic transformation in a manner similar to that induced by the full length MSK1 protein. The overall results suggest that the CTD MSK1 is regulated by a novel, αL-helix-independent mechanism, suggesting that a diverse mechanism of autoinhibition and activation might be adopted by members of closely related protein kinase family.