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Rat brain myo-inositol 3-phosphate synthase is a phosphoprotein |
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| Authors: | R N Parthasarathy J Lakshmanan M Thangavel R S Seelan J I Stagner A J Janckila R E Vadnal M F Casanova L K Parthasarathy |
| Institution: | 1. Molecular Neuroscience and Bioinformatics Laboratories, Mental Health, Behavioral Science and Research Services, Robley Rex Veterans Affairs Medical Center, 800 Zorn Avenue (151), Louisville, KY, 40206, USA 2. Department of Biochemistry and Molecular Biology, University of Louisville, 319 Abraham Flexner Way, Louisville, KY, 40202, USA 3. Department of Psychiatry and Behavioral Sciences, University of Louisville, 501 East Broadway, Louisville, KY, 40202, USA 4. Price Institute of Surgical Research, Department of Surgery, School of Medicine, University of Louisville, 511 S. Floyd St, Louisville, KY, 40202, USA 5. Department of Molecular, Cellular & Craniofacial Biology, School of Dentistry, University of Louisville, 501, South Preston Street, Louisville, KY, 40202, USA 6. Research Services, Robley Rex Veterans Affairs Medical Center, 800 Zorn Avenue (151), Louisville, KY, 40206, USA 7. Special Hematology Lab, Robley Rex Veterans Affairs Medical Center, Louisville, KY, 40202, USA 8. Department of Microbiology and Immunology, School of Medicine, University of Louisville, Louisville, KY, 40202, USA 9. Eastern Colorado Health Care System, Department of Veterans Affairs, 4112, Outlook Blvd, Pueblo, CO, 81008, USA |
| 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. |
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