Identification of Protein Kinase B (PKB) as a Phosphatidylinositol 3,4,5-Trisphosphate Binding Protein in Dictyostelium discoideum

Abstract

  We have searched for phosphatidylinositol (PI)-3,4,5-trisphosphate (PIP₃) binding proteins in Dictyostelium discoideum using beads bearing a PIP₃ analogue, PIP₃-APB. One of the binding proteins with a molecular mass of 55 kDa was purified and its amino acid sequence was partially amalyzed. Database searches showed that the analyzed sequence was identical to that of protein kinase B (PKB) of D. discoideum. The specific activity of D. discoideum PKB, when expressed together with constitutively active PI-3 kinase in mammalian cells, was elevated by about three-fold, suggesting that PKB could also act downstream of PI-3 kinase in Dictyostelium cells.