title: Rat brain myo-inositol 3-phosphate synthase is a phosphoprotein.
abstract: The therapeutic effects of lithium in bipolar disorder are poorly understood. Lithium decreases free inositol levels by inhibiting inositol monophosphatase 1 and myo-inositol 3-phosphate synthase (IPS). In this study, we demonstrate for the first time that IPS can be phosphorylated. This was evident when purified rat IPS was dephosphorylated by lambda protein phosphatase and analyzed by phospho-specific ProQ-Diamond staining and Western blot analysis. These techniques demonstrated a mobility shift consistent with IPS being phosphorylated. Mass spectral analysis revealed that Serine-524 (S524), which resides in the hinge region derived from exon 11 of the gene, is the site for phosphorylation. Further, an antibody generated against a synthetic peptide of IPS containing monophosphorylated-S524, was able to discriminate the phosphorylated and non-phosphorylated forms of IPS. The phosphoprotein is found in the brain and testis, but not in the intestine. The intestinal IPS isoform lacks the peptide bearing S524, and hence, cannot be phosphorylated. Evidences suggest that IPS is monophosphorylated at S524 and that the removal of this phosphate does not alter its enzymatic activity. These observations suggest a novel function for IPS in brain and other tissues. Future studies should resolve the functional role of phospho-IPS in brain inositol signaling.
authors.affiliation: Molecular Neuroscience and Bioinformatics Laboratories, Mental Health, Behavioral Science and Research Services, Robley Rex Veterans Affairs Medical Center, Louisville, KY 40206, USA. ranga.parthasarathy@va.gov
authors.forename: R N
authors.initials: RN
authors.lastname: Parthasarathy
authors.forename: J
authors.initials: J
authors.lastname: Lakshmanan
authors.forename: M
authors.initials: M
authors.lastname: Thangavel
authors.forename: R S
authors.initials: RS
authors.lastname: Seelan
authors.forename: J I
authors.initials: JI
authors.lastname: Stagner
authors.forename: A J
authors.initials: AJ
authors.lastname: Janckila
authors.forename: R E
authors.initials: RE
authors.lastname: Vadnal
authors.forename: M F
authors.initials: MF
authors.lastname: Casanova
authors.forename: L K
authors.initials: LK
authors.lastname: Parthasarathy
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D000906:Antibodies / Q000737:chemistry; D001921:Brain / Q000201:enzymology*; D007422:Intestines / Q000201:enzymology; D019753:Intramolecular Lyases / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D008970:Molecular Weight; D009928:Organ Specificity; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology; D010750:Phosphoproteins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000737:chemistry / Q000378:metabolism; D013737:Testis / Q000201:enzymology
chemical_list: D000906:Antibodies; D007527:Isoenzymes; D010446:Peptide Fragments; D010750:Phosphoproteins; D012694:Serine; D019753:Intramolecular Lyases; C105497:D-myo-inositol-3-phosphate synthase