Selenol (-SeH) as a target for mercury and gold in biological systems: Contributions of mass spectrometry and atomic spectroscopy

The selenol (-SeH) group of selenocysteine (SeCys), a cysteine analogue and a more potent nucleophile, has often been considered as a potential target of toxic trace metals and metalloids (Hg, As) and metal-lodrugs (Au, Pt), privileged with regard to more abundant aminoacids, such as cysteine or histidine. However, the formal evidence of the occurrence of the Se-metal bond, the involvement of selenol and the exact location of the Se-metal bonds in proteins containing several SeCys residues, especially in vivo, have largely been missing. This review discusses critically the contributions of the state-of-the-art analytical mass spectrometric and atomic spectroscopic techniques to studies of metal-binding sites with the different level of confidence in terms of demonstration of the occurrence of the Se-metal binding and the location of the binding site within the Se-containing molecule. They include methods indicating potential interactions on the basis of evidence of co-elution (HPLC-ICP MS) and co-localisation (laser ablation ICP MS, XRF, nanoSIMS) of selenium and the metal(s), methods confirming the evidence of the formation of Se-containing molecule - metal adducts (electrospray and MALDI MS), methods proving the existence of the actual Se-Me bond (EXAFS and XANES) and, finally, methods able to identify the actual binding site in proteins containing several SeCys residues (top-down MS, MS of tryptic digests of metal-protein adducts). The state of the art of in-vitro studies of metal-ion interactions with model SeCys-containing compounds at different levels of molecular complexity (selenoproteins, mimics selenopeptides, selenocysteine) and oxidation (Se-Se, Se-S bridges) as well as that of in-vivo studies are critically reviewed.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This review critically discusses the actual location of Se-metal bonds and the involvement of selenol in proteins containing multiple SeCys residues. It also examines the applications of advanced mass spectrometric and atomic spectroscopic techniques in studying metal-binding sites.