Structural and biochemical analysis of human inositol monophosphatase-1 inhibition by ebselen

Abstract

Bipolar disorder is a major psychiatric disorder associated with cognitive impairment and a high suicide rate. Frontline therapy for this condition includes lithium (Li⁺)-containing treatments that can exert severe side effects. One target of Li⁺ is inositol monophosphatase-1 (IMPase1); inhibition of IMPase1 through small-molecule compounds may provide an alternative treatment for bipolar disorder. One such compound is the anti-inflammatory drug ebselen, which is well tolerated and safe; however, ebselen’s exact mechanism of action in IMPase1 inhibition is not fully understood, preventing rational design of IMPase1 inhibitors. To fill this gap, we performed crystallographic and biochemical studies to investigate how ebselen inhibits IMPase1. We obtained a structure of IMPase1 in space group P2₁ after treatment with ebselen that revealed three key active-site loops (residues 33–44, 70–79, and 161–165) that are either disordered or in multiple conformations, supporting a hypothesis whereby dynamic conformational changes may be important for catalysis and ebselen inhibition. Using the thermal shift assay, we confirmed that ebselen significantly destabilizes the enzyme. Molecular docking suggests that ebselen could bind in the vicinity of His217. Investigation of the role of IMPase1 residues His217 and Cys218 suggests that inhibition of IMPase1 by ebselen may not be mediated via covalent modification of the active-site cysteine (Cys218) and is not affected by the covalent modification of other cysteine residues in the structure. Our results suggest that effects previously ascribed to ebselen-dependent inhibition likely result from disruption of essential active-site architecture, preventing activation of the IMPase1–Mg²⁺ complex.

Communicated by Ramaswamy H. Sarma

Keywords:

• Ebselen
• human inositol monophosphatase-1
• mechanism of inhibition
• active-site architecture

Acknowledgments

This work was supported by an allocation of computing time from Jordan’s National Supercomputing Center (IMAN1). We thank Zaid Abudayyeh (IMAN1, Amman) for excellent IT support, Tamara Sabri for excellent technical assistance, and Greg Papadakos and Jürgen Brem for their help in protein purification. We thank Michael McDonough for fruitful discussion of the structure and for his comments on the final manuscript. We thank Diamond Light Source for beamtime. This manuscript was written during sabbatical leave of AA from the University of Jordan.

Author contributions

All authors discussed the results and contributed to the final manuscript. AA and GC conceived and designed the work. NS and AR prepared the IMPase1 constructs. AR performed enzyme assays and chemical modification. EL collected X-ray data. AA performed protein purification, thermal shift assays, crystallization, and X-ray data refinement and interpretation. SN and SR performed HPLC measurements. AA and NL preformed data interpretation and wrote the main manuscript text. All authors reviewed the manuscript.

Data availability statement

The datasets used and/or analysed during the current study available from the corresponding authors on reasonable request.

Disclosure statement

The authors declare no competing interests.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.