title: Structure of a human inositol 1,4,5-trisphosphate 3-kinase: substrate binding reveals why it is not a phosphoinositide 3-kinase.
abstract: Mammalian cells produce a variety of inositol phosphates (InsPs), including Ins(1,4,5)P3 that serves both as a second messenger and as a substrate for inositol polyphosphate kinases (IPKs), which further phosphorylate it. We report the structure of an IPK, the human Ins(1,4,5)P3 3-kinase-A, both free and in complexes with substrates and products. This enzyme catalyzes transfer of a phosphate from ATP to the 3-OH of Ins(1,4,5)P3, and its X-ray crystal structure provides a template for understanding a broad family of InsP kinases. The catalytic domain consists of three lobes. The N and C lobes bind ATP and resemble protein and lipid kinases, despite insignificant sequence similarity. The third lobe binds inositol phosphate and is a unique four-helix insertion in the C lobe. This lobe embraces all of the phosphates of Ins(1,4,5)P3 in a positively charged pocket, explaining the enzyme's substrate specificity and its inability to phosphorylate PtdIns(4,5)P2, the membrane-resident analog of Ins(1,4,5)P3.
authors.affiliation: MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, United Kingdom.
authors.forename: Beatriz
authors.initials: B
authors.lastname: González
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Schell
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Letcher
authors.forename: Dmitry B
authors.initials: DB
authors.lastname: Veprintsev
authors.forename: Robin F
authors.initials: RF
authors.lastname: Irvine
authors.forename: Roger L
authors.initials: RL
authors.lastname: Williams
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D020816:Amino Acid Motifs / Q000502:physiology; D000595:Amino Acid Sequence / Q000502:physiology; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D020134:Catalytic Domain / Q000502:physiology; D058544:Class Ib Phosphatidylinositol 3-Kinase; D018360:Crystallography, X-Ray; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry; D010716:Phosphatidylinositols / Q000737:chemistry*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D007527:Isoenzymes; D010716:Phosphatidylinositols; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); C051038:Inositol 1,4,5-trisphosphate 3-kinase; D058544:Class Ib Phosphatidylinositol 3-Kinase; C546760:PIK3CG protein, human