Dynamics of the essential trace element selenium in mammals and molecular basis for selenoprotein biosynthesis

点击翻译按钮获取中文摘要

Selenium is an essential trace element with a variety of physiological role and is strictly discriminated from its cognate sulfur to be incorporated into a specific position of proteins as a selenocysteine residue. Mammalian cells are proposed to contain 25 selenoproteins. Selenocysteine residues are not directly synthesized from free selenocysteine but are biosynthesized from an active form of selenium which is formed from selenocysteine by decomposition at the translation step. In the current study, we identified factors involved in selenoprotein biosynthesis in mammalian cells and analyzed their functions.1. We identified nucleolin and RAD17 as novel proteins which sqiecifically recognize and bind to selenocysteine insertion sequence (SECTS).2. Selenccystiene lyase (SCL) decomposes L-selenocysteine to form selenium and L-alanine and is involved in selenoprotein biosynthesis. We salved X-ray crystal structure of SCL from rat in the native form and in the complexed form with L-cysteine. In the structure of SCL complexed with L-cysteine, the thiol group of L-cysteine was coordinated to bind to PLP-lysine Shiff base of the enzyme. The result suggest that Cys 375 of SCL plays an important role in the strict substrate specificity of the enzyme toward L-selenocysteine.3. We constructed the mutants of selenophosphate synthetase (SeID) from Escherichia coli by site directed mutagenesis. The analysis showed that a highly conserved cysteine residue (Cys17) of SeID is essential for the catalytic activity of the enzyme.