title: The activity of barley NADPH-dependent thioredoxin reductase C is independent of the oligomeric state of the protein: tetrameric structure determined by cryo-electron microscopy.
abstract: Thioredoxin and thioredoxin reductase can regulate cell metabolism through redox regulation of disulfide bridges or through removal of H(2)O(2). These two enzymatic functions are combined in NADPH-dependent thioredoxin reductase C (NTRC), which contains an N-terminal thioredoxin reductase domain fused with a C-terminal thioredoxin domain. Rice NTRC exists in different oligomeric states, depending on the absence or presence of its NADPH cofactor. It has been suggested that the different oligomeric states may have diverse activity. Thus, the redox status of the chloroplast could influence the oligomeric state of NTRC and thereby its activity. We have characterized the oligomeric states of NTRC from barley (Hordeum vulgare L.). This also includes a structural model of the tetrameric NTRC derived from cryo-electron microscopy and single-particle reconstruction. We conclude that the tetrameric NTRC is a dimeric arrangement of two NTRC homodimers. Unlike that of rice NTRC, the quaternary structure of barley NTRC complexes is unaffected by addition of NADPH. The activity of NTRC was tested with two different enzyme assays. The N-terminal part of NTRC was tested in a thioredoxin reductase assay. A peroxide sensitive Mg-protoporphyrin IX monomethyl ester (MPE) cyclase enzyme system of the chlorophyll biosynthetic pathway was used to test the catalytic ability of both the N- and C-terminal parts of NTRC. The different oligomeric assembly states do not exhibit significantly different activities. Thus, it appears that the activities are independent of the oligomeric state of barley NTRC.
authors: Carlsberg Laboratory, Gamle Carlsberg vej 10, DK-1799 Copenhagen V, Denmark.
authors: Ragna Peterson
authors: RP
authors: Wulff
authors: Joakim
authors: J
authors: Lundqvist
authors: Gudrun
authors: G
authors: Rutsdottir
authors: Andreas
authors: A
authors: Hansson
authors: Anne
authors: A
authors: Stenbaek
authors: Dominika
authors: D
authors: Elmlund
authors: Hans
authors: H
authors: Elmlund
authors: Poul Erik
authors: PE
authors: Jensen
authors: Mats
authors: M
authors: Hansson
mesh_terms: D020285:Cryoelectron Microscopy / Q000379:methods; D018360:Crystallography, X-Ray / Q000379:methods; D019281:Dimerization; D001467:Hordeum / Q000201:enzymology*; D008274:Magnesium / Q000737:chemistry; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D009249:NADP / Q000737:chemistry*; D010084:Oxidation-Reduction; D010545:Peroxides / Q000737:chemistry; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D013880:Thioredoxin-Disulfide Reductase / Q000737:chemistry*; D013879:Thioredoxins / Q000737:chemistry
chemical_list: D010545:Peroxides; D011994:Recombinant Proteins; D013879:Thioredoxins; D009249:NADP; D013880:Thioredoxin-Disulfide Reductase; D008274:Magnesium