Abstract
MEK1 and MEK2 are closely related, dual-specificity tyrosine/threonine protein kinases found in the Ras/Raf/MEK/ERK mitogen-activated protein kinase (MAPK) signaling pathway. Approximately 30% of all human cancers have a constitutively activated MAPK pathway, and constitutive activation of MEK1 results in cellular transformation. Here we present the X-ray structures of human MEK1 and MEK2, each determined as a ternary complex with MgATP and an inhibitor to a resolution of 2.4 Å and 3.2 Å, respectively. The structures reveal that MEK1 and MEK2 each have a unique inhibitor-binding pocket adjacent to the MgATP-binding site. The presence of the potent inhibitor induces several conformational changes in the unphosphorylated MEK1 and MEK2 enzymes that lock them into a closed but catalytically inactive species. Thus, the structures reported here reveal a novel, noncompetitive mechanism for protein kinase inhibition.
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Acknowledgements
We thank M. Dumond for assistance in the crystallization of MEK1, and N. Ahn, B. Lunney, B. Finzel and N. Chirgadze for their thoughtful review of the manuscript. Use of the IMCA-CAT beamline 17-ID at the Advanced Photon Source was supported by the companies of the Industrial Macromolecular Crystallography Association through a contract with Illinois Institute of Technology. Use of the Advanced Photon Source was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. W-31-109-Eng-38.
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Supplementary information
Supplementary Fig. 1
Unbiased electron density map of the MEK1 active site. (PDF 58 kb)
Supplementary Fig. 2
Mass distribution computed for the MEK, MgATP and PD318088 ternary complexes from analytical ultracentrifugation results. (PDF 110 kb)
Supplementary Fig. 3
Interference data from sedimentation equilibrium at 13 °C of the ternary complex of PD318088, MgATP with MEK1 (a, b) and MEK2 (c, d). (PDF 171 kb)
Supplementary Fig. 4
Multiple sequence alignment of the kinase domain of human MEK1 versus other members of the MKK family. (PDF 303 kb)
Supplementary Table 1
Apparent disassociation constants obtained from fitting the sedimentation equilibrium data for apo MEK1 and the ternary complex. (PDF 23 kb)
Supplementary Table 2
Apparent disassociation constants obtained from fitting the sedimentation equilibrium data for apo MEK2 and the ternary complex. (PDF 20 kb)
Supplementary Table 3
X–ray data collection and refinement statistics. (PDF 20 kb)
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Ohren, J., Chen, H., Pavlovsky, A. et al. Structures of human MAP kinase kinase 1 (MEK1) and MEK2 describe novel noncompetitive kinase inhibition. Nat Struct Mol Biol 11, 1192–1197 (2004). https://doi.org/10.1038/nsmb859
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DOI: https://doi.org/10.1038/nsmb859
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