2bji
High Resolution Structure of myo-Inositol Monophosphatase, The Target of Lithium Therapy
Structural highlights
FunctionIMPA1_BOVIN Responsible for the provision of inositol required for synthesis of phosphatidylinositol and polyphosphoinositides and has been implicated as the pharmacological target for lithium action in brain. Has broad substrate specificity and can use myo-inositol monophosphates, myo-inositol 1,3-diphosphate, myo-inositol 1,4-diphosphate, scyllo-inositol-phosphate, glucose-1-phosphate, glucose-6-phosphate, fructose-1-phosphate, beta-glycerophosphate, and 2'-AMP as substrates (By similarity). Is equally active with myo-inositol monophosphate and D-galactose 1-phosphate.[UniProtKB:P29218][1] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedInositol monophosphatase is a key enzyme of the phosphatidylinositol signalling pathway and the putative target of the mood-stabilizing drug lithium. The crystal structure of bovine inositol monophosphatase has been determined at 1.4 A resolution in complex with the physiological magnesium ion ligands. Three magnesium ions are octahedrally coordinated at the active site of each of the two subunits of the inositol monophosphatase dimer and a detailed three-metal mechanism is proposed. Ligands to the three metals include the side chains of Glu70, Asp90, Asp93 and Asp220, the backbone carbonyl group of Ile92 and several solvent molecules, including the proposed nucleophilic water molecule (W1) ligated by both Mg-1 and Mg-3. Modelling of the phosphate moiety of inositol monophosphate to superpose the axial phosphate O atoms onto three active-site water molecules orientates the phosphoester bond for in-line attack by the nucleophilic water which is activated by Thr95. Modelling of the pentacoordinate transition state suggests that the 6-OH group of the inositol moiety stabilizes the developing negative charge by hydrogen bonding to a phosphate O atom. Modelling of the post-reaction complex suggests a role for a second water molecule (W2) ligated by Mg-2 and Asp220 in protonating the departing inositolate. This second water molecule is absent in related structures in which lithium is bound at site 2, providing a rationale for enzyme inhibition by this simple monovalent cation. The higher resolution structural information on the active site of inositol monophosphatase will facilitate the design of substrate-based inhibitors and aid in the development of better therapeutic agents for bipolar disorder (manic depression). High-resolution structure of myo-inositol monophosphatase, the putative target of lithium therapy.,Gill R, Mohammed F, Badyal R, Coates L, Erskine P, Thompson D, Cooper J, Gore M, Wood S Acta Crystallogr D Biol Crystallogr. 2005 May;61(Pt 5):545-55. Epub 2005, Apr 20. PMID:15858264[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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