Selenoprotein Biosynthesis and Selenium-Specific Enzymes

Abstract

Selenocysteine lyase (SCL) is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that specifically acts on L-selenocysteine to yield L-alanine and selenium. The enzyme does not act on L-cysteine at all. We have recently found that RNAi-mediated depletion of SCL results in significant reductions in activities and protein levels of the selenoproteins glutathione peroxidase and thioredoxin reductase, suggesting an important cellular role of SCL in selenoprotein synthesis. Therefore, the strict discrimination between selenium and sulfur by SCL may be a key step in the specific seleniumdelivery pathway for selenoprotein synthesis. However, the mechanism for the discrimination between selenium and sulfur by SCL remains unclear. In this review, we describe function and mechanism of SCL involved in the biosynthesis of selenoprotein. We also discuss the catalytic properties of the SCL-related enzymes, cysteine desulfurases.