Prin, a photometric Raf indicator
K. Terai and M. Matsuda. Ras binding opens c-Raf to expose the docking site for MEK. EMBO Rep. 6:251-255, 2005.
A key signaling molecule, c-Raf, is situated downstream from Ras and upstream from the mitogen-activated protein kinase (MAPK) kinase (MEK). To study the mechanism underlying the signal transduction from Ras to MEK, we developed probes based on the principle of fluorescence resonance energy transfer (FRET).
In agreement with previous models, it was found that c-Raf adopted two conformations: open active and closed inactive. Ras binding induced the c-Raf transition from closed to open conformation, which enabled c-Raf to bind to MEK. In the presence of a cytosolic Ras mutant, c-Raf bound to, but failed to phosphorylate, MEK in the cytoplasm. In contrast, the cytosolic Ras mutant significantly enhanced MEK phosphorylation by a membrane-targeted c-Raf. These results demonstrated the essential role of Ras-induced conformational change in MEK activation by c-Raf.
The video image of Raf activation is below.