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 nonidentical protein kinase domains in one polypeptide. We present the active conformation of the crystal structures of its C-terminal kinase domain in apo form and in complex with a nonhydrolyzable ATP analogue at 2.0 Å and 2.5 Å resolutions, 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 the C-terminal kinase domain of MSK1, the C-terminal α-helix is located in the surface groove, but forms no hydrogen bonds with the substrate-binding loop or nearby helices, and does not interfere with the protein's autophosphorylation activity. Mutational analysis confirmed that the α-L-helix is inherently nonautoinhibitory. 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 C-terminal kinase domain of 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 a closely related protein kinase family.
Bibliographical noteFunding Information:
This work was funded by The Hormel Foundation and by National Institutes of Health grants CA027502 , CA077646 , CA120388 , R37CA08164 , and ES016548 . Part of this work was based on research conducted at the Northeastern Collaborative Access Team beamline 24ID of the APS and was supported by award RR-15301 from the National Center for Research Resources at the National Institutes of Health. Use of the APS was supported by the US Department of Energy, Office of Basic Energy Sciences, under contract no. DE-AC02-06CH11357. Part of the work was conducted at the Canadian Light Source (Canadian Macromolecular Crystallography Facility).
- Active form
- Autoinhibitory helix
- Crystal structure
- Protein kinase