Mechanism of the regulation of type IB phosphoinositide 3OH-kinase byG-protein betagamma subunits.
Type IB phosphoinositide 3OH-kinase (PI3K) is activated by G-protein betagamma subunits (Gbetagammas). The enzyme is soluble and largely cytosolic in vivo. Its substrate, PtdIns(4,5)P(2), and the Gbetagammas are localized at the plasma membrane. We have addressed the mechanism by which Gbetagammas regulate the PI3K using an in vitro approach. We used sedimentation assays and surface plasmon resonance to determine association of type IB PI3K with lipid monolayers and vesicles of varying compositions, some of which had Gbetagammas incorporated. Association and dissociation rate constants were determined. Our results indicated that in an assay situation in vitro the majority of PI3K will be associated with lipid vesicles, irrespective of the presence or absence of Gbetagammas. In line with this, a constitutively active membrane-targeted PI3K construct could still be activated substantially by Gbetagammas in vitro. We conclude that Gbetagammas activate type IB PI3K by a mechanism other than translocation to the plasma membrane.
Krugmann
Sonja
S
Signalling Programme, The Babraham Institute, Babraham, Cambridge CB2 4AT, U.K.
Cooper
Matthew A
MA
Williams
Dudley H
DH
Hawkins
Phillip T
PT
Stephens
Len R
LR
D000818:Animals; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D019281:Dimerization; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000378:metabolism*; D018411:Spodoptera; D020349:Surface Plasmon Resonance; D014162:Transfection
D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D020962:Heterotrimeric GTP-Binding Proteins; D019869:Phosphatidylinositol 3-Kinases; D021122:Protein Subunits; D011994:Recombinant Proteins; C118981:G-protein Beta gamma