Privileged Incorporation of Selenium as Selenocysteine in Lactobacillus reuteri Proteins Demonstrated by Selenium-specific Imaging and Proteomics

Abstract

An analytical approach was developed to study the incorporation of selenium (Se), an important trace element involved in the protection of cells from oxidative stress, into the well-known probiotic Lactobacillus reuteri Lb2 BM-DSM 16143. The analyses revealed that about half of the internalized Se was covalently incorporated into soluble proteins. Se-enriched proteins were detected in 2D gels by laser ablation inductively coupled plasma mass spectrometry imaging (LA-ICP MSI) and identified by capillary HPLC with the parallel ICP MS ( 78 Se) and electrospray Orbitrap MS/MS detection. On the basis of the identification of 10 richest in selenium proteins, it was demonstrated that selenium was incorporated by the strain exclusively as selenocysteine. Also, the exact location of selenocysteine within the primary sequence was determined. This finding is in a striking contrast to another common nutraceutical, Se-enriched yeast, which incorporates Se principally as selenomethionine. Molecular & Cellular

Selenium effects on the metabolism of a Se-metabolizingLactobacillus reuteri: analysis of envelope-enriched and extracellular proteomes

“…54 It can be hypothesized that this enzyme could act as a selenium storage protein, as already suggested by Ogasawara and co-workers. 55 Both glyceraldehyde 3-phosphate dehydrogenase and phosphoketolase were already identified in the in toto proteome 28 as selenocysteine-containing proteins: this result corroborates once more the ability of the strain to fix selenium generating organic Se-forms and can explain the previously reported increase of Se concentration in the external medium after about 6 hours of growth. 28 Furthermore, the fact that SeCyscontaining proteins are released in the extracellular environment before cell lysis is an added value for a probiotic strain to be employed as a nutraceutical, since this mechanism increases selenium bioavailability in the human gut.…”

“…55 Both glyceraldehyde 3-phosphate dehydrogenase and phosphoketolase were already identified in the in toto proteome 28 as selenocysteine-containing proteins: this result corroborates once more the ability of the strain to fix selenium generating organic Se-forms and can explain the previously reported increase of Se concentration in the external medium after about 6 hours of growth. 28 Furthermore, the fact that SeCyscontaining proteins are released in the extracellular environment before cell lysis is an added value for a probiotic strain to be employed as a nutraceutical, since this mechanism increases selenium bioavailability in the human gut. In fact it has to be considered that only organic Se forms (selenocysteine and/or selenomethionine) can be metabolized and assimilated by humans without inducing toxic effects, actually representing the most bio-available form for human body.…”

“…In these maps, image analysis revealed 59 spots that were then identified by nano-LC-chip MS/MS as 21 different proteins (considering isoforms). 28 the ability of the strain to fix selenium into seven proteins in the form of selenocysteine (SeCys, U), the presence of selenopeptides in the extracellular secreted proteins from selenium-grown bacteria was manually checked in the raw data of the LC-MS/MS. This analysis revealed the presence of two peptides containing a SeCys and belonging, respectively, to glyceraldehyde 3-phosphate dehydrogenase (spot 8, NDGVDFVLE À UTGFYTSAEK) and phosphoketolase (spot 19, NQE À UINLFVTSK) (Fig.…”

Selenite-stress selected mutant strains of probiotic bacteria for Se source production

“…multivitamin preparations, weight-loss products, protein mixes, 39 infant formulas and animal feed, sodium selenite and sodium 40 selenate are usually supplemented [5]. As selenate (SeO 4 2− ) and 41 selenite (SeO 3 2− ) are highly water soluble ions, at high concentra-42 tion they are toxic but less toxic than selenide (Se 2− ) and having 43 tendency to bioaccumulate [6]. Both the bioreduction of SeO 3 2− to 44 nontoxic and biologically available elementary selenium (Se 0 ) and 45 the incorporation of this transition metal into organic selenium 46 compounds (mainly selenocystein) have been demonstrated in 47 bacterial cultures (e.g.…”

Glyphosate, pathways to modern diseases IV: cancer and related pathologies

“…Lactobacillus reuteri is a popular species in probiotics, shown to be effective against diarrhoea in children [211], and to inhibit the prooxidant cytokine TNF-α in humans [212]. This species has been found to be especially effective in its ability to produce selenocysteine, and has been proposed to have therapeutic benefit in cases of selenium deficiency [213]. Lactobacillus is especially vulnerable to glyphosate due to its crucial and unusual need for manganese as an antioxidant [214,215], so it is plausible that diminished Lactobacillus representation in the gut could lead to an impaired supply of selenocysteine for the thyroid.…”