title: Heterologous expression and enzymatic properties of a selenium-independent glutathione peroxidase from the parasitic nematode Brugia pahangi.
abstract: A full-length cDNA from the parasitic nematode Brugia pahangi encoding a secreted homolog of glutathione peroxidase in which the codon for the active site selenocysteine is substituted naturally by a cysteine codon has been expressed in Spodoptera frugiperda (insect) cells via Autographa californica nuclear polyhedrosis virus (baculovirus). The recombinant protein was glycosylated and secreted from the cells in tetrameric form. The purified protein showed glutathione peroxidase activity with a range of organic hydroperoxides, including L-alpha-phosphatidylcholine hydroperoxide, but no significant activity against hydrogen peroxide. Glutathione was the only thiol tested that served as a substrate for the enzyme, which showed no activity with the thioredoxin system (thioredoxin, thioredoxin reductase, and NADPH). No glutathione-conjugating activity was detected against a range of electrophilic compounds that are common substrates for glutathione S-transferases. The apparent (pseudo)m for glutathione was determined as 4.9 mM at a fixed concentration of linolenic acid hydroperoxide (3 microM). The enzyme showed low affinity for hydroperoxide substrates (apparent Km for linolenic acid hydroperoxide and L-alpha-phosphatidylcholine hydroperoxide of 3.8 and 9.7 mM, respectively at a fixed glutathione concentration of 3 mM).
authors.affiliation: Department of Biochemistry, Imperial College of Science, Technology and Medicine, London, United Kingdom.
authors.forename: L
authors.initials: L
authors.lastname: Tang
authors.forename: K
authors.initials: K
authors.lastname: Gounaris
authors.forename: C
authors.initials: C
authors.lastname: Griffiths
authors.forename: M E
authors.initials: ME
authors.lastname: Selkirk
mesh_terms: D000818:Animals; D001483:Base Sequence; D017179:Brugia pahangi / Q000201:enzymology* / Q000235:genetics; D002478:Cells, Cultured; D005979:Glutathione Peroxidase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006031:Glycosylation; D015801:Helminth Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008042:Linolenic Acids / Q000378:metabolism; D008054:Lipid Peroxides / Q000378:metabolism; D008969:Molecular Sequence Data; D017924:Nucleopolyhedroviruses / Q000235:genetics; D010713:Phosphatidylcholines / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D012643:Selenium / Q000378:metabolism*; D018411:Spodoptera / Q000166:cytology; D013379:Substrate Specificity
chemical_list: D015801:Helminth Proteins; D008042:Linolenic Acids; D008054:Lipid Peroxides; D010713:Phosphatidylcholines; D011994:Recombinant Proteins; C057590:phosphatidylcholine hydroperoxide; C025998:13-hydroperoxylinolenic acid; D005979:Glutathione Peroxidase; C080439:selenium-independent glutathione peroxidase; D012643:Selenium