A novel monothiol glutaredoxin (Grx4) from Escherichia coli can serve as a substrate for thioredoxin reductase.
Glutaredoxins are ubiquitous proteins that catalyze the reduction of disulfides via reduced glutathione (GSH). Escherichia coli has three glutaredoxins (Grx1, Grx2, and Grx3), all containing the classic dithiol active site CPYC. We report the cloning, expression, and characterization of a novel monothiol E. coli glutaredoxin, which we name glutaredoxin 4 (Grx4). The protein consists of 115 amino acids (12.7 kDa), has a monothiol (CGFS) potential active site and shows high sequence homology to the other monothiol glutaredoxins and especially to yeast Grx5. Experiments with gene knock-out techniques showed that the reading frame encoding Grx4 was essential. Grx4 was inactive as a GSH-disulfide oxidoreductase in a standard glutaredoxin assay with GSH and hydroxyethyl disulfide in a complete system with NADPH and glutathione reductase. An engineered CGFC active site mutant did not gain activity either. Grx4 in reduced form contained three thiols, and treatment with oxidized GSH resulted in glutathionylation and formation of a disulfide. Remarkably, this disulfide of Grx4 was a direct substrate for NADPH and E. coli thioredoxin reductase, whereas the mixed disulfide was reduced by Grx1. Reduced Grx4 showed the potential to transfer electrons to oxidized E. coli Grx1 and Grx3. Grx4 is highly abundant (750-2000 ng/mg of total soluble protein), as determined by a specific enzyme-link immunosorbent assay, and most likely regulated by guanosine 3',5'-tetraphosphate upon entry to stationary phase. Grx4 was highly elevated upon iron depletion, suggesting an iron-related function for the protein.
Fernandes
Aristi Potamitou
AP
Medical Nobel Institute for Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-171 77 Stockholm, Sweden.
Fladvad
Malin
M
Berndt
Carsten
C
Andrésen
Cecilia
C
Lillig
Christopher Horst
CH
Neubauer
Peter
P
Sunnerhagen
Maria
M
Holmgren
Arne
A
Vlamis-Gardikas
Alexios
A
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D001665:Binding Sites; D002474:Cell-Free System; D002942:Circular Dichroism; D003001:Cloning, Molecular; D004220:Disulfides / Q000737:chemistry; D004583:Electrons; D004797:Enzyme-Linked Immunosorbent Assay; D004926:Escherichia coli / Q000201:enzymology / Q000378:metabolism*; D005838:Genotype; D054477:Glutaredoxins; D005978:Glutathione / Q000737:chemistry; D006159:Guanosine Tetraphosphate / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D013058:Mass Spectrometry; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D009249:NADP / Q000737:chemistry; D016366:Open Reading Frames; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics*; D010100:Oxygen / Q000737:chemistry; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry; D013379:Substrate Specificity; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013696:Temperature; D013880:Thioredoxin-Disulfide Reductase / Q000737:chemistry* / Q000378:metabolism; D013997:Time Factors
D000596:Amino Acids; D004220:Disulfides; D054477:Glutaredoxins; D011994:Recombinant Proteins; D013438:Sulfhydryl Compounds; D006159:Guanosine Tetraphosphate; D009249:NADP; D007501:Iron; D010088:Oxidoreductases; D013880:Thioredoxin-Disulfide Reductase; D005978:Glutathione; D010100:Oxygen