title: Inositol polyphosphate multikinase regulates inositol 1,4,5,6-tetrakisphosphate.
abstract: The human inositol phosphate multikinase (IPMK, 5-kinase) has a preferred 5-kinase activity over 3-kinase and 6-kinase activities and a substrate preference for inositol 1,3,4,6-tetrakisphosphate (Ins(1,3,4,6)P4) over inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) and inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4). We now report that the recombinant human protein can catalyze the conversion of inositol 1,4,5,6-tetrakisphosphate (Ins(1,4,5,6)P4) to Ins(1,3,4,5,6)P5 in vitro; the reaction product was identified by HPLC to be Ins(1,3,4,5,6)P5. The apparent Vmax was 42 nmol of Ins(1,3,4,5,6)P5 formed/min/mg protein, and the apparent Km was 222 nM using Ins(1,3,4,6)P4 as a substrate; the catalytic efficiency was similar to that for Ins(1,4,5)P3. Stable over-expression of the human protein in HEK-293 cells abrogates the in vivo elevation of Ins(1,4,5,6)P4 from the Salmonella dublin SopB protein. Hence, the human 5-kinase may also regulate the level of Ins(1,4,5,6)P4 and have an effect on chloride channel regulation.
authors.affiliation: Department of Internal Medicine, Division of Hematology, Box 8125, Washington University, School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Shao-Chun
authors.initials: SC
authors.lastname: Chang
authors.forename: Philip W
authors.initials: PW
authors.lastname: Majerus
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D002384:Catalysis; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D007700:Kinetics; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D007295:Inositol Phosphates; D011994:Recombinant Proteins; C451920:inositol-1,3,4,5,6-pentakisphosphate; C081651:inositol-1,4,5,6-tetrakisphosphate; D017853:Phosphotransferases (Alcohol Group Acceptor); C434257:inositol polyphosphate multikinase; C489224:SopB protein, Salmonella