Molecular characterization of glutathione peroxidase-like protein in halotolerant Chlamydomonas sp W80

A cDNA clone encoding a glutathione peroxidase (GPX)-like protein was isolated from the cDNA library from halotolerant Chlamydomonas W80 (C . W80) by a simple screening method based on the bacterial expression system. The cDNA clone contained an open reading frame encoding a mature protein of 163 amino acids with a calculated molecular mass of 18 267 Da. No potential signal peptide was found. The deduced amino acid sequence of the cDNA showed 40-63% and 37-46% homology to those of GPX-like proteins from higher plants and mammalian GPXs, respectively. The C. W80 GPX-like protein contained a normal cysteine residue instead of a selenocysteine at the catalytic site. However, it contained amino acid residues (glutamine and tryptophan) that are involved in three protein loops and are important for the catalytic activity in the mammalian GPX. Interestingly, the native and recombinant GPX-like proteins showed activities towards unsaturated fatty acid hydroperoxides, but not towards either H-2 O-2 or phospholipid hydroperoxide. Transformed E. coli cells expressing the C . W80 GPX-like protein showed enhanced tolerance to 5% NaCl or 0.2 mM paraquat treatments. Accession number : The nucleotide sequence data reported have been submitted to the DDBJ, EMBL, and GenBank nucleotide sequence databases with the following accession number AB009083.