Florie Schild
Biochemical characterization and involvement in the stress response of "Selenium Binding Protein 1" protein (SBP1) in Arabidopsis thaliana
Published on 29 November 2013
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Thesis presented November 29, 2013
Abstract :
The function of the protein “Selenium binding protein 1” (SBP1), present in almost all organisms, is not yet well established. This protein has numerous potential metal binding sites. In
Arabidopsis thaliana, SBP1 overexpression increases tolerance to two toxic compounds for the plant, cadmium (Cd) and selenium (Se), which are often found as soil pollutants. For a better understanding of SBP1 function and its involvement in detoxification mechanisms, an integrated approach combining
in vitro and
in planta experiments, has been performed. Biochemical characterization of SBP1 has revealed its chelating properties to different ligands including Cd and Se. Cd is bound to SBP1 with a metal ion to protein molar ratio of 3 and a KD of 2.2 × 10-7 M mainly
via sulfur-containing amino acids and potentially histidine residues. Se from SeO32- can covalently bound SBP1 with a ligand to protein molar ratio of 1. This binding occurs
via cysteines 21 and 22 and forms a R-S-Se-S-R complex.
In planta analyses have shown that SBP1 is cytosolic and nuclear. The use of bioluminescent lines allowed the identification of a GAGAC motif in the
SBP1 promoter region. This motif is a sulfur starvation responsive element and a major
cis element involved in SBP1 expression in response to stress, including Cd and Se. The result directly links SBP1 function to an enhanced sulfur demand of the cell. SBP1 overexpression in plants disturbs Se accumulation in shoots but not its speciation. All together these results strongly suggest that SBP1 could act as a detoxifying protein through its chelating properties and plays a role in S/Se metabolisms.
Keywords:
Cadmium, selenium, toxicity, biochemical characterization, Arabidopsis
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