Specific phosphopeptide binding regulates a conformational change in the PI 3-kinase SH2 domain associated with enzyme activation.

摘要: SH2 (src-homology 2) domains define a newly recognized binding motif that mediates the physical association of target phosphotyrosyl proteins with downstream effector enzymes. An example such phosphoprotein-effector coupling is provided by phosphatidylinositol 3-kinase (PI 3-kinase) specific phosphorylation sites within PDGF receptor, c-Src/polyoma virus middle T antigen complex and insulin receptor substrate IRS-1. Notably, phosphoprotein p85 also stimulates an increase in catalytic activity PI p110 subunit, which can be mimicked phosphopeptides corresponding to targeted sites. To investigate how domain activation, we have examined differential effects phosphotyrosine receptor-, IRS-1- c-Src-derived on conformation isolated 3-kinase. Although both activating non-activating bind domain, higher affinity induce qualitatively distinct conformational change as monitored CD NMR spectroscopy. Amide proton exchange protease protection assays further show high affinity, phosphopeptide induces non-local dynamic stabilization. Based these findings propose subunit structure transmitted regulates enzymatic allosteric mechanism.