Delivery of selenium to selenophosphate synthetase for selenoprotein biosynthesis.

BACKGROUND: Selenophosphate, the key selenium donor for the synthesis of selenoprotein and selenium-modified tRNA, is produced by selenophosphate synthetase (SPS) from ATP, selenide, and H2O. Although free selenide can be used as the in vitro selenium substrate for selenophosphate synthesis, the precise physiological system that donates in vivo selenium substrate to SPS has not yet been characterized completely. SCOPE OF REVIEW: In this review, we discuss selenium metabolism with respect to the delivery of selenium to SPS in selenoprotein biosynthesis. MAJOR CONCLUSIONS: Glutathione, selenocysteine lyase, cysteine desulfurase, and selenium-binding proteins are the candidates of selenium delivery system to SPS. The thioredoxin system is also implicated in the selenium delivery to SPS in Escherichia coli. GENERAL SIGNIFICANCE: Selenium delivered via a protein-bound selenopersulfide intermediate emerges as a central element not only in achieving specific selenoprotein biosynthesis but also in preventing the occurrence of toxic free selenide in the cell. This article is part of a Special Issue entitled "Selenium research in biochemistry and biophysics - 200 year anniversary".