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Nature. 2019 Oct 3. doi: 10.1038/s41586-019-1660-y. [Epub ahead of print]

Architecture of autoinhibited and active BRAF-MEK1-14-3-3 complexes.

Park E1,2, Rawson S2, Li K1,2, Kim BW1,2, Ficarro SB1,3,4, Pino GG1,2, Sharif H1,2, Marto JA1,3,4, Jeon H5,6, Eck MJ7,8.

Author information

1
Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA, USA.
2
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA.
3
Blais Proteomics Center, Dana-Farber Cancer Institute, Boston, MA, USA.
4
Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, Boston, MA, USA.
5
Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA, USA. hjeon@crystal.harvard.edu.
6
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA. hjeon@crystal.harvard.edu.
7
Department of Cancer Biology, Dana-Farber Cancer Institute, Boston, MA, USA. eck@crystal.harvard.edu.
8
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, USA. eck@crystal.harvard.edu.

Abstract

RAF family kinases are RAS-activated switches that initiate signalling through the MAP kinase cascade to control cellular proliferation, differentiation and survival1-3. RAF activity is tightly regulated and inappropriate activation is a frequent cause of cancer4-6; however, the structural basis for RAF regulation is poorly understood at present. Here we use cryo-electron microscopy to determine autoinhibited and active-state structures of full-length BRAF in complexes with MEK1 and a 14-3-3 dimer. The reconstruction reveals an inactive BRAF-MEK1 complex restrained in a cradle formed by the 14-3-3 dimer, which binds the phosphorylated S365 and S729 sites that flank the BRAF kinase domain. The BRAF cysteine-rich domain occupies a central position that stabilizes this assembly, but the adjacent RAS-binding domain is poorly ordered and peripheral. The 14-3-3 cradle maintains autoinhibition by sequestering the membrane-binding cysteine-rich domain and blocking dimerization of the BRAF kinase domain. In the active state, these inhibitory interactions are released and a single 14-3-3 dimer rearranges to bridge the C-terminal pS729 binding sites of two BRAFs, which drives the formation of an active, back-to-back BRAF dimer. Our structural snapshots provide a foundation for understanding normal RAF regulation and its mutational disruption in cancer and developmental syndromes.

PMID:
31581174
DOI:
10.1038/s41586-019-1660-y

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