Abstract
We previously found that selenium is essential for growth of coccolithophorids (Haptophyte algae). Selenium is also an essential element for animals as a constituent of selenoproteins. In the present study, we identified the selenoprotein in a coccolithophorid, Emiliania huxleyi, and tried to elucidate the physiological function of selenium in this alga. Six kinds of selenoproteins (SEP1 to 6) were found in E. huxleyi cells. We analyzed the cDNA-sequence of SEP2 by RT-PCR using degenerate primers. A BLAST analysis of the deduced amino acid sequence revealed homology to protein disulfide isomerase (PDI), especially around the thioredoxin domain. SEP2 cDNA contained in frame TGA codon, that codes selenocysteine, at the position corresponding to cysteine residue at the reaction center of PDI in other organisms. These results suggest that, in a coccolithophorid, selenium may be specially participated in folding and assembling pathways of proteins as a component of PDI.
