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.
Copyright 2004 Cell Press
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adenosine Triphosphate / metabolism*
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Amino Acid Motifs / physiology
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Amino Acid Sequence / physiology
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Animals
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Binding Sites / physiology
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Catalytic Domain / physiology
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Class Ib Phosphatidylinositol 3-Kinase
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Crystallography, X-Ray
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Humans
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Inositol 1,4,5-Trisphosphate / metabolism*
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Isoenzymes / chemistry
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Models, Molecular
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Molecular Sequence Data
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Molecular Structure
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Phosphatidylinositol 3-Kinases / chemistry
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Phosphatidylinositols / chemistry*
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Phosphorylation
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Phosphotransferases (Alcohol Group Acceptor) / chemistry*
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Phosphotransferases (Alcohol Group Acceptor) / metabolism*
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Protein Binding / physiology*
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Protein Structure, Tertiary / physiology
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Sequence Homology, Amino Acid
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Substrate Specificity
Substances
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Isoenzymes
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Phosphatidylinositols
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Inositol 1,4,5-Trisphosphate
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Adenosine Triphosphate
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Phosphatidylinositol 3-Kinases
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Phosphotransferases (Alcohol Group Acceptor)
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Inositol 1,4,5-trisphosphate 3-kinase
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Class Ib Phosphatidylinositol 3-Kinase
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PIK3CG protein, human
Associated data
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PDB/1W2C
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PDB/1W2D
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PDB/1W2F