title: G Protein beta gamma subunits act on the catalytic domain to stimulate Bruton's agammaglobulinemia tyrosine kinase.
abstract: G proteins are critical cellular signal transducers for a variety of cell surface receptors. Both alpha and betagamma subunits of G proteins are able to transduce receptor signals. Several direct effect molecules for Gbetagamma subunits have been reported; yet the biochemical mechanism by which Gbetagamma executes its modulatory role is not well understood. We have shown that Gbetagamma could directly increase the kinase activity of Bruton's tyrosine kinase (Btk) whose defects are responsible for X chromosome-linked agammaglobulinemia in patients. The well characterized interaction of Gbetagamma with the PH (pleckstrin homology)/TH (Tec-homology) module of Btk was proposed to be the underlying activation mechanism. Here we show that Gbetagamma also interacts with the catalytic domain of Btk leading to increased kinase activity. Furthermore, we showed that the PH/TH module is required for Gbetagamma-induced membrane translocation of Btk. The membrane anchorage is also dependent on the interaction of Btk with phosphatidylinositol 3,4,5-trisphosphate, the product of phosphoinositide 3-kinase. These data support a dual role for Gbetagamma in the activation of Btk signaling function, namely membrane translocation and direct regulation of Btk catalytic activity.
authors.affiliation: Department of Physiology, Weill Medical College of Cornell University, New York, New York 10021, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Lowry
authors.forename: Xin-Yun
authors.initials: XY
authors.lastname: Huang
mesh_terms: D000077329:Agammaglobulinaemia Tyrosine Kinase; D000361:Agammaglobulinemia / Q000201:enzymology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D020134:Catalytic Domain; D002460:Cell Line; D016895:Culture Media, Serum-Free; D017930:Genes, Reporter; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011485:Protein Binding; D021122:Protein Subunits; D011505:Protein-Tyrosine Kinases / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D016895:Culture Media, Serum-Free; D021122:Protein Subunits; D011993:Recombinant Fusion Proteins; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human; D020962:Heterotrimeric GTP-Binding Proteins