Bipolar-disorder (manic-depressive illness) is a severe chronic illness affecting ~1% of the adult population. It is treated with mood-stabilizers, the prototypic one being lithium-salts (lithium), but it has life threatening side-effects and a significant number of patients fail to respond. The lithium-inhibitable enzyme inositol-monophosphatase (IMPase) is one of the viable targets for lithium's mechanism of action. Calbindin-D28k (calbindin) up-regulates IMPase activity. The IMPase-calbindincomplex was modeled using the program MolFit. The in-silico model indicated that the 55-66 amino-acid segment of IMPase anchors calbindin via Lys59 and Lys61 with a glutamate in between (Lys-Glu-Lys motif) and that the motif interacts with residues Asp24 and Asp26 of calbindin. We found that differently from wildtype calbindin, IMPase was not activated by mutated calbindin in which Asp24 and Asp26 were replaced by alanine. Calbindin's effect was significantly reduced by a linear peptide with the sequence of amino acids 58-63 of IMPase (peptide 1) and by six amino-acid linear peptides including at least part of the Lys-Glu-Lys motif. The three amino-acid peptide Lys-Glu-Lys or five amino-acid linear peptides containing this motif were ineffective. Mice administered peptide 1 intracerebroventricularly exhibited a significant anti-depressant-like reduced immobility in the forced-swim test. Based on the sequence of peptide 1, and to potentially increase the peptide's stability, cyclic and linear pre-cyclic analog peptides were synthesized. One cyclic peptide and one linear pre-cyclic analog peptide inhibited calbindin-activated brain IMPase activity in-vitro. Our findings may lead to the development of molecules capable of inhibiting IMPase activity at an alternative site than that of lithium.
Bibliographical noteFunding Information:
Funding for this study was provided by a Stanley Foundation research grant, a NOFAR grant from the Israeli Ministry of Industry, Trade and Labor and by an R&D grant from Johnson & Johnson to OA and GA. OA received a Young Research Grant from the Israeli Institute for Psychobiology for part of this study.
The authors acknowledge the intellectual contribution of Dr. Alon Shamir, a previous Ph.D. student of GA in the Department of Clinical Biochemistry and pharmacology and the Psychiatry Research Unit, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel who initiated the calbindin project in the lab. The study was supported by a Stanley Foundation research grant, a NOFAR grant from the Israeli Ministry of Industry, Trade and Labor and by an R&D grant from Johnson & Johnson to OA and GA. OA received a Young Research Grant from the Israeli Institute for Psychobiology for part of this study.
- Bipolar disorder
- Inositol monophosphatase
- Protein-protein docking