Selenoproteome Expression Studied by Non-Radioactive Isotopic Selenium-Labeling in Human Cell Lines

Selenoproteins, in which the selenium atom is present in the rare amino acid selenocysteine, are vital components of cell homeostasis, antioxidant defense, and cell signaling in mammals. The expression of the selenoproteome, composed of 25 selenoprotein genes, is strongly controlled by the selenium status of the body, which is a corollary of selenium availability in the food diet. Here, we present an alternative strategy for the use of the radioactive ⁷⁵Se isotope in order to characterize the selenoproteome regulation based on (i) the selective labeling of the cellular selenocompounds with non-radioactive selenium isotopes (⁷⁶Se, ⁷⁷Se) and (ii) the detection of the isotopic enrichment of the selenoproteins using size-exclusion chromatography followed by inductively coupled plasma mass spectrometry detection. The reliability of our strategy is further confirmed by western blots with distinct selenoprotein-specific antibodies. Using our strategy, we characterized the hierarchy of the selenoproteome regulation in dose–response and kinetic experiments.

Detection of Selenoproteins by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP MS) in Immobilized pH Gradient (IPG) Strips

In contrast to other trace elements that are cofactors of enzymes and removed from proteins under denaturing conditions, Se is covalently bound to proteins when incorporated into selenoproteins, since it is a component of selenocysteine aminoacid. It implies that selenoproteins can undergo several biochemical separation methods in stringent and chaotropic conditions and still maintain the presence of selenium in the primary sequence. This feature has been used to develop a method for the detection of trace levels of human selenoproteins in cell extracts without the use of radioactive isotopes. The selenoproteins are separated as a function of their isoelectric point (pI) using iso-electrofocusing (IEF) electrophoretic strips and detected by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP MS). This method, therefore referred to as IEF-LA-ICP MS, allowed the detection of several selenoproteins in human cell lines, including Gpx1, Gpx4, TXNRD1, TXNRD2, and SELENOF.

Comparison of analytical methods using enzymatic activity, immunoaffinity and selenium-specific mass spectrometric detection for the quantitation of glutathione peroxidase 1

Glutathione peroxidase 1 (Gpx1), one of the most responsive selenoproteins to the variation of selenium concentration, is often used to evaluate "selenium status" at a cellular or organismal level. The four major types of analytical methodologies to quantify Gpx1 were revisited. They include (i) an enzymatic assay, (ii, iii) polyacrylamide gel electrophoresis (PAGE) with (ii) western blot detection of protein or (iii) inductively coupled plasma mass spectrometry (ICP MS) detection of selenium, and (iv) size-exclusion chromatography with ICP MS detection. Each of the four methods was optimized for the quantification of Gpx1 with maximum sensitivity. The methods based on the enzymatic and immunodetection offer a much higher sensitivity but their accuracy is compromised by the limited selectivity and limited dynamic range. The advantages, drawbacks and sources of error of each technique are critically discussed and the need for the cross-validation of the results using the different techniques to assure the quality assurance of quantitative analysis is emphasized.

The high yielding synthesis of pillar[5]arenes under Friedel-Crafts conditions explained by dynamic covalent bond formation

Systematic investigations of the cyclooligomerization of 1,4-disubstituted hydroquinone derivatives under Friedel-Crafts conditions have been carried out to demonstrate that the formation of pillar[5]arenes occurs under thermodynamic control.