title: Improved yields for baculovirus-mediated expression of human His(6)-PDK1 and His(6)-PKBbeta/Akt2 and characterization of phospho-specific isoforms for design of inhibitors that stabilize inactive conformations.
abstract: PDK1 and PKB/Akt have a pleckstrin homology (PH) domain at the C-terminus and N-terminus, respectively, which stabilizes an unphosphorylated, autoinhibited conformation. Binding of the PH domain to a phospholipid second messenger causes relief of autoinhibition, which results in kinase phosphorylation and activation. Baculovirus-mediated expression in Sf9 insect cells of both His(6)-PDK1 and His(6)-PKBbeta/Akt2 were optimized, which significantly improved the yields (5-fold) of the affinity purified enzymes over previously reported values. Isoelectric focusing (IEF) and Western analyses indicated that the apparent V(max)=192+/-13 U/mg and K(m) (PDK-Tide)=55+/-10 microM of purified His(6)-PDK1 results from a mixture of at least three different phospho-specific isoforms (pI values of 6.8, 6.5, and 6.4). A purely unphosphorylated isoform of His(6)-PDK1 (pI=6.8) was generated by treatment with lambda protein phosphatase (lambdaPP), which decreased V(max) to 2.4+/-0.4 U/mg and increased K(m) (PDK-Tide) to 217+/-61 microM. Isoelectric focusing and Western analyses indicated that the apparent V(max)=0.21+/-0.03 U/mg and K(m) (Crosstide)=87+/-30 microM of purified His(6)-PKBbeta/Akt2 results from a mixture of the enzyme monophosphorylated either at Ser-474 ( approximately 90%) or at Thr-309 ( approximately 10%). A purely unphosphorylated isoform of His(6)-PKBbeta/Akt2 (pI=6.4) was generated by treatment with lambdaPP, which decreased V(max) approximately 2-fold. The optimization of high-level production and detailed characterization of purified and lambdaPP-treated His(6)-PDK1 and His(6)-PKBbeta/Akt2 will facilitate detailed structural and kinetic studies aimed at understanding the mechanism of second messenger-induced activation.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, P.O. Box 016129 (R-629), Miami, FL 33101-6129, USA.
authors.forename: Xinxin
authors.initials: X
authors.lastname: Gao
authors.forename: Peggy
authors.initials: P
authors.lastname: Yo
authors.forename: Thomas K
authors.initials: TK
authors.lastname: Harris
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D016367:Baculoviridae / Q000378:metabolism; D003001:Cloning, Molecular; D004789:Enzyme Activation; D004795:Enzyme Stability; D006801:Humans; D007525:Isoelectric Focusing; D008968:Molecular Conformation; D010766:Phosphorylation; D020033:Protein Isoforms / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification; D015398:Signal Transduction
chemical_list: D020033:Protein Isoforms; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578562:PDPK1 protein, human; D017346:Protein Serine-Threonine Kinases