Biochemical Characterization of Full-Length Oncogenic BRAF together with Molecular Dynamics Simulations Provide Insight into the Activation and Inhibition Mechanisms of RAF Kinases.

The most prevalent BRAF mutation, V600E, occurs frequently in melanoma and other cancers. Although extensive progress has been made toward understanding the biology of RAF kinases, little in vitro characterization of full-length BRAF is available. Herein, we show the successful purification of active, full-length BRAF from mammalian cells for in vitro experiments. Our biochemical characterization of intact BRAF together with molecular dynamics (MD) simulations of the BRAF kinase domain and cell-based assays demonstrate that BRAF has several unique features that contribute to its tumorigenesis. Firstly, steady-state kinetic analyses reveal that purified BRAF is more active than fully activated wild-type BRAF; this is consistent with the notion that elevated signaling output is necessary for transformation. Secondly, BRAF has a higher potential to form oligomers, despite the fact that the V600E substitution confers constitutive kinase activation independent of an intact side-to-side dimer interface. Thirdly, BRAF bypasses inhibitory P-loop phosphorylation to enforce the necessary elevated signaling output for tumorigenesis. Together, these results provide new insight into the biochemical properties of BRAF , complementing the understanding of BRAF regulation under normal and disease conditions.