Dynamics of the phosphoinositide 3-kinase p110? interaction with p85? and membranes reveals aspects of regulation distinct from p110?.

ABSTRACT: Phosphoinositide 3-kinase ? is upregulated in lymphocytic leukemias. Because the p85-regulatory subunit binds to any class IA subunit, it was assumed there is a single universal p85-mediated regulatory mechanism; however, we find isozyme-specific inhibition by p85?. Using deuterium exchange mass spectrometry (DXMS), we mapped regulatory interactions of p110? with p85?. Both nSH2 and cSH2 domains of p85? contribute to full inhibition of p110?, the nSH2 by contacting the helical domain and the cSH2 via the C terminus of p110?. The cSH2 inhibits p110? and p110?, but not p110?, implying that p110? is uniquely poised for oncogenic mutations. Binding RTK phosphopeptides disengages the SH2 domains, resulting in exposure of the catalytic subunit. We find that phosphopeptides greatly increase the affinity of the heterodimer for PIP2-containing membranes measured by FRET. DXMS identified regions decreasing exposure at membranes and also regions gaining exposure, indicating loosening of interactions within the heterodimer at membranes.

SUBMITTER: Burke JE 

PROVIDER: S-EPMC3155019 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature