title: Expression of selenocysteine-containing glutathione S-transferase in Escherichia coli.
abstract: Evolution of a probable 'glutathione-binding ancestor' resulting in a common thioredoxin-fold for glutathione S-transferases and glutathione peroxidases may possibly suggest that a glutathione S-transferase could be engineered into a selenium-containing glutathione S-transferase (seleno-GST), having glutathione peroxidase (GPX) activity. Here, we addressed this question by production of such protein. In order to obtain a recombinant seleno-GST produced in Escherichia coli, we introduced a variant bacterial-type selenocysteine insertion sequence (SECIS) element which afforded substitution with selenocysteine for the catalytic Tyr residue in the active site of GST from Schistosoma japonica. Utilizing coexpression with the bacterial selA, selB, and selC genes (encoding selenocysteine synthase, SelB, and tRNA(Sec), respectively) the yield of recombinant seleno-GST was about 2.9 mg/L bacterial culture, concomitant with formation of approximately 85% truncation product as a result of termination of translation at the selenocysteine-encoding UGA codon. The mutations inferred as a result of the introduction of a SECIS element did not affect the glutathione-binding capacity (Km = 53 microM for glutathione as compared to 63 microM for the wild-type enzyme) nor the GST activity (kcat = 14.3 s(-1) vs. 16.6 s(-1)), provided that the catalytic Tyr residue was intact. When this residue was changed to selenocysteine, however, the resulting seleno-GST lost the GST activity. It also failed to display any novel GPX activity towards three standard peroxide substrates (hydrogen peroxide, butyl hydroperoxide or cumene hydroperoxide). These results show that recombinant selenoproteins with internal selenocysteine residues may be heterologously produced in E. coli at sufficient amounts for purification. We also conclude that introduction of a selenocysteine residue into the catalytic site of a glutathione S-transferase is not sufficient to induce GPX activity in spite of a maintained glutathione-binding capacity.
authors.affiliation: Key Laboratory for Molecular Enzymology and Engineering of the Ministry of Education, Jilin University, Changchun 130023, PR China.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Jiang
authors.forename: Elias S J
authors.initials: ES
authors.lastname: Arnér
authors.forename: Ying
authors.initials: Y
authors.lastname: Mu
authors.forename: Linda
authors.initials: L
authors.lastname: Johansson
authors.forename: Jinming
authors.initials: J
authors.lastname: Shi
authors.forename: Siqi
authors.initials: S
authors.lastname: Zhao
authors.forename: Shujun
authors.initials: S
authors.lastname: Liu
authors.forename: Ruiying
authors.initials: R
authors.lastname: Wang
authors.forename: Tianzhu
authors.initials: T
authors.lastname: Zhang
authors.forename: Ganglin
authors.initials: G
authors.lastname: Yan
authors.forename: Junqiu
authors.initials: J
authors.lastname: Liu
authors.forename: Jiacong
authors.initials: J
authors.lastname: Shen
authors.forename: Guimin
authors.initials: G
authors.lastname: Luo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005982:Glutathione Transferase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010957:Plasmids; D017433:Protein Structure, Secondary; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012549:Schistosoma japonicum / Q000201:enzymology / Q000235:genetics; D017279:Selenocysteine / Q000032:analysis*
chemical_list: D029968:Escherichia coli Proteins; D012329:RNA, Bacterial; D011993:Recombinant Fusion Proteins; D017279:Selenocysteine; D005982:Glutathione Transferase