Far-reaching effects of tyrosine64 phosphorylation on Ras revealed with BeF3– complexes.

Tyrosine phosphorylation on Ras by Src kinase is known to uncouple Ras from upstream regulation and downstream communication. However, the mechanisms by which phosphorylation modulates these interactions have not been detailed. Here, the major mono-phosphorylation level on tyrosine64 is quantified by 31P NMR and mutagenesis. Crystal structures of unphosphorylated and tyrosine64-phosphorylated Ras in complex with a BeF3− ground state analogue reveal "closed" Ras conformations very different from those of the "open" conformations previously observed for non-hydrolysable GTP analogue structures of Ras. They deliver new mechanistic and conformational insights into intrinsic GTP hydrolysis. Phosphorylation of tyrosine64 delivers conformational changes distant from the active site, showing why phosphorylated Ras has reduced affinity to its downstream effector Raf. 19F NMR provides evidence for changes in the intrinsic GTPase and nucleotide exchange rate and identifies the concurrent presence of a major "closed" conformation alongside a minor yet functionally important "open" conformation at the ground state of Ras. This study expands the application of metal fluoride complexes in revealing major and minor conformational changes of dynamic and modified Ras proteins. Protein tyrosine kinase Src is known to phosphorylate Ras protein on tyrosine32 and 64, and uncouple Ras from the signaling cascade, however, the mechanisms through which phosphorylation modulates these interactions remain poorly understood. Here, the authors quantify the major mono-phosphorylation level on tyrosine64 by 31P NMR and mutagenesis, and reveal the key conformational changes of phosphorylated Ras using BeF3− complexes by X-ray crystallography and 19F NMR, providing new mechanistic and conformational insights into Ras dynamics regulation. [ABSTRACT FROM AUTHOR]