2005 Volume 22 Pages 147-152
Selenium is an essential trace element for mammals, birds, and some bacteria. Its remarkable biological effects in eukaryotes may be related to unique functions of various selenoproteins. Selenoprotein biosynthesis requires monoselenophospahte, which is synthesized from selenide and ATP by selenophosphate synthetase (SPS). In the present study, Sps1 and Sps2 genes were cloned from a cDNA library of the lung adenocarcinoma cells NCI-H441. The inframe TGA codon of the lung Sps2 was genetically altered to TGT (Cys) to obtain Sps2Cys gene. The human lung Sps homologs were characterized by an in vivo complementation assay using a ∆selD mutant host strain. A low-salt medium optimized for in vivo selD-complementation assay allowed recombinant Sps2Cys to effectively complement the selD mutation. In contrast, only a weak complementation by the Sps1 gene was observed when selenite was the selenium source. Better complementation by Sps1 was observed with L-SeCys, suggesting the involvement of a selenocysteine β-lyase for mobilization of selenium. The results of the complementation study suggested that Sps1 encoded enzyme that functions on selenocysteine recycling whereas the Sps2 enzyme can function as a de novo selenite assimilation system.
