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Nat Struct Mol Biol. 2008 May;15(5):452-61. doi: 10.1038/nsmb.1418. Epub 2008 May 4.

Membrane-dependent signal integration by the Ras activator Son of sevenless.

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Department of Molecular and Cell Biology, and Howard Hughes Medical Institute, QB3 Institute, 176 Stanley Hall, University of California, Berkeley, California 94720, USA.

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  • Nat Struct Mol Biol.2008 Jun;15(6): 651.


The kinetics of Ras activation by Son of sevenless (SOS) changes profoundly when Ras is tethered to membranes, instead of being in solution. SOS has two binding sites for Ras, one of which is an allosteric site that is distal to the active site. The activity of the SOS catalytic unit (SOS(cat)) is up to 500-fold higher when Ras is on membranes compared to rates in solution, because the allosteric Ras site anchors SOS(cat) to the membrane. This effect is blocked by the N-terminal segment of SOS, which occludes the allosteric site. We show that SOS responds to the membrane density of Ras molecules, to their state of GTP loading and to the membrane concentration of phosphatidylinositol-4,5-bisphosphate (PIP2), and that the integration of these signals potentiates the release of autoinhibition.

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