Selenium speciation analysis of Misgurnus anguillicaudatus selenoprotein by HPLC–ICP–MS and HPLC–ESI–MS/MS

Selenium in Peptide Chemistry

In recent years, researchers have been exploring the potential of incorporating selenium into peptides, as this element possesses unique properties that can enhance the reactivity of these compounds. Selenium is a non-metallic element that has a similar electronic configuration to sulfur. However, due to its larger atomic size and lower electronegativity, it is more nucleophilic than sulfur. This property makes selenium more reactive toward electrophiles. One of the most significant differences between selenium and sulfur is the dissociation of the Se-H bond. The Se-H bond is more easily dissociated than the S-H bond, leading to higher acidity of selenocysteine (Sec) compared to cysteine (Cys). This difference in acidity can be exploited to selectively modify the reactivity of peptides containing Sec. Furthermore, Se-H bonds in selenium-containing peptides are more susceptible to oxidation than their sulfur analogs. This property can be used to selectively modify the peptides by introducing new functional groups, such as disulfide bonds, which are important for protein folding and stability. These unique properties of selenium-containing peptides have found numerous applications in the field of chemical biology. For instance, selenium-containing peptides have been used in native chemical ligation (NCL). In addition, the reactivity of Sec can be harnessed to create cyclic and stapled peptides. Other chemical modifications, such as oxidation, reduction, and photochemical reactions, have also been applied to selenium-containing peptides to create novel molecules with unique biological properties.

LC/ICP-MS AND COMPLEMENTARY TECHNIQUES IN BESPOKE AND NONTARGETED SPECIATION ANALYSIS OF ELEMENTS IN FOOD SAMPLES

Chemical elements speciation analysis of food samples has been among the most important scientific topics over the last decades. Food samples are comprised of high variety of chemical compounds, from which many can interact with metals and metalloids, forming complex elemental species with various influence on the human body. It is particularly important not only to determine the amount of certain chemical element in food sample but also to identify the form in which given element occurs in given sample. Employment of bespoke and nontargeted speciation methods, with the use of liquid chromatography inductively coupled plasma mass spectrometry (LC/ICP-MS) and complementary techniques, provides more complete picture on the metals and metalloids speciation in food. This review discusses issues concerning speciation analysis of metals and metalloids in food samples with the use of LC/ICP-MS as a leading technique in elemental speciation nowadays and a complimentary technique intended for their identification. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Selenium-Containing Proteins/Peptides from Plants: A Review on the Structures and Functions

Selenium is an essential microelement required for biological processes. Traditional selenium supplements (selenite and selenomethionine mainly) remain concerns due to toxicity and bioavailability. In recent decades, biofortification strategies have been applied to produce selenium-enriched edible plants to address the challenges of superior nutritional quality requirements. Plant-derived selenium-containing proteins/peptides offer potential health benefits beyond the basic nutritional requirements of Se. Highly nucleophilic seleno-amino acids, special peptide sequences, and favorable bioavailability contribute to the biological activities of selenium-containing proteins/peptides, such as antioxidant, antihypertensive, anti-inflammatory, and immunomodulatory effects. However, their applications on a commercial scale are insufficient owing to the complexity of purification and identification techniques and the sparse information on bioavailability and metabolism. In this review, selenium status, structural features, bioactivities, structure-activity relationships, and bioavailability, as well as the mechanisms underlying the bioactivities and metabolism of plant-derived selenium-containing proteins/peptides, are summarized and discussed for their nutraceutical use.

Expanding beyond ICP-MS to better understand selenium biochemistry

Selenium is an essential trace element in human health and therefore its concentration in biological samples (biofluids and tissues) is used as an indicator of health and nutritional status. In humans, selenium's biological activity occurs through the 25 identified selenoproteins. As total selenium concentration encompasses both functional selenoproteins, small selenocompounds and other selenium-binding proteins, selenium speciation, rather than total concentration, is critical in order to assess functional selenium. Previously, quantitative analysis of selenoproteins required laborious techniques that were often slow and costly. However, more recent advancements in tandem mass spectrometry have facilitated the qualitative and quantitative identification of these proteins. In light of the current alternatives for understanding selenium biochemistry, we aim to provide a review of the modern applications of electrospray ionisation mass spectrometry (ESI-MS) as an alternative to inductively coupled plasma mass spectrometry (ICP-MS) for qualitative and quantitative selenium speciation.

Speciation Analysis of Selenium in Candida utilis Yeast Cells Using HPLC-ICP-MS and UHPLC-ESI-Orbitrap MS Techniques

Selenium plays a key role in the proper metabolism of living organisms. The search for new selenium compounds opens up new possibilities for understanding selenometabolome in yeast cells. This study was aimed at the identification of compounds containing selenium in the feed yeasts Candida utilis ATCC 9950. Yeast biomass was kept in aqueous solutions enriched with inorganic selenium (20 mg·L−1) for 24 h. Speciation analysis of the element was performed using the HPLC-ICP-MS and UHPLC-ESI-Orbitrap MS techniques. The obtained selenium value in the yeast was 629 μg·g−1, while the selenomethionine value was 31.57 μg·g−1. The UHPLC-ESI-Orbitrap MS analysis conducted allowed for the identification of six selenium compounds: dehydro-selenomethionine-oxide, selenomethionine, selenomethionine-NH3, a Se-S conjugate of selenoglutathione-cysteine, methylthioselenoglutathione, and 2,3-DHP-selenocysteine-cysteine. In order to explain the structure of selenium compounds, the selected ions were subjected to fragmentation. The selenium compounds obtained with a low mass play a significant role in the metabolism of the compound. However, the bioavailability of such components and their properties have not been fully understood. The number of signals indicating the presence of selenium compounds obtained using the UHPLC-ESI-Orbitrap MS method was characterized by higher sensitivity than when using the HPLC-ICP-MS method. The obtained results will expand upon knowledge about the biotransformation of selenium in eukaryotic yeast cells. Future research should focus on understanding the entire selenium metabolism in cells and on the search for new transformation pathways for this element. This opens up new possibilities for obtaining functional food, rich in easily absorbable selenium sources, and constituting an alternative to dietary supplements based on this compound found primarily in inorganic form.