Characterization of Human Selenocysteine Synthase Involved in Selenoprotein Biosynthesis

抄録

Bacterial selenocysteine synthase is a pyridoxal 5'-phosphate-dependent enzyme that catalyzes the conversion of seryl-tRNA^Sec to selenocysteyl-tRNA^Sec for selenoprotein biosynthesis. Human selenocysteine synthase(SecS),originally annotated as SLA/LP, was previously reported to operate in selenocysteyl-tRNA^Sec synthesis, but the mechanism of conversion from Ser-tRNA^Sec by the eukaryotic enzyme remained unresolved. Herein, the human cDNA encoding SecS has been cloned and overexpressed in Escherichia coli. SecS was co-purified with E. coli tRNAs, which was revealed to contain tRNA^Sec by PCR analysis. The purified enzyme exhibited a UV-visible absorption maximum at 420 nm characteristic of pyridoxal 5'-phosphate-dependent enzymes. In vitro selenocysteyl-tRNA^Sec synthesis assay suggests that the formation of phosphoseryl-tRNA^Sec is essential for human seryl-tRNA^Sec, but not archaeal seryl-tRNA^Sec to be converted to selenocysteyl-tRNA^Sec by human SecS.