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Molecular functions of selenoproteinN (SelenoN)

SelenoN molecular function remains unknown up to now and we use multiple approaches to investigate it.

In vivo study

To address SelenoN function in vivo we generated the Selenon-/--null mouse model by gene targeting. The Selenon-/- mice had normal growth and lifespan and were indistinguishable from wild-type mice. However when submitted to challenging physical exercises like forced swimming tests, the Selenon-/- mice developed an obvious phenotype characterized by limited motility and body rigidity during the swimming session as well as a progressive curvature of the spine and predominant alteration of paravertebral muscles. The Selenon-/- mice phenotype recapitulates the muscular symptoms described in patients with SELENON-related myopathy. It is a valuable tool to dissect the role of SelenoproteinN (SelenoN) in muscle function and to characterize the pathophysiological process. See Fig. 1

Figure 1. Spectrum of mutations in SELENON-related myopathy patients and Selenon-/- mice model.

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d’après Flanigan et al. 2000
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d’après Rederstorff et al. 2011

Structural approach

As illustrated on Figure2, the SelenoN protein is a glycosylated transmembrane protein, localized in the endoplasmic reticulum. Recombinant forms of SelenoN proteins have been expressed in different systems. Purified proteins will be used for biochemical in vitro enzymatic assays as well as crystallographic and structure-function relation analyses.

Photo of microscopy SelenoN
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Figure 2: Cellular localization of SelenoN and schematic representation of the various motifs and domains predicted in the SelenoN protein sequence by bioinformatic analysis.

Molecular study – Characterization of the selenoN interactome

The purified engineered proteins are studied by means of biochemical and biophysical methods (enzymatic tests, western, spectrophotometric or spectrofluorimetric titration, mass spectrometry) to identify the substrates, ligands or cofactors likely to interact with the protein. The high molecular complexes formed in cellulo within the membrane of the endoplasmic reticulum are also analyzed after purification, using SelenoN mutants whose amino-acids in the catalytic site were modified to trap disulfide reaction intermediates.