Structure of Hordeum vulgare NADPH-dependent thioredoxin reductase 2. Unwinding the reaction mechanism

Journal Article · Tue Sep 01 04:00:00 EDT 2009 · Acta Crystallographica. Section D: Biological Crystallography

DOI:https://doi.org/10.1107/S0907444909021817· OSTI ID:22347952

Kirkensgaard, Kristine G. ^[1]; Hägglund, Per; Finnie, Christine; Svensson, Birte ^[2]; Henriksen, Anette ^[1]

---

1. Carlsberg Laboratory (Denmark)
2. Enzyme and Protein Chemistry, Department of Systems BioIogy, Technical University of Denmark (Denmark)

The first crystal structure of a cereal NTR, a protein involved in seed development and germination, has been determined. The structure is in a conformation that excludes NADPH binding and indicates that a domain reorientation facilitated by Trx binding precedes NADPH binding in the reaction mechanism. Thioredoxins (Trxs) are protein disulfide reductases that regulate the intracellular redox environment and are important for seed germination in plants. Trxs are in turn regulated by NADPH-dependent thioredoxin reductases (NTRs), which provide reducing equivalents to Trx using NADPH to recycle Trxs to the active form. Here, the first crystal structure of a cereal NTR, HvNTR2 from Hordeum vulgare (barley), is presented, which is also the first structure of a monocot plant NTR. The structure was determined at 2.6 Å resolution and refined to an R{sub cryst} of 19.0% and an R{sub free} of 23.8%. The dimeric protein is structurally similar to the structures of AtNTR-B from Arabidopsis thaliana and other known low-molecular-weight NTRs. However, the relative position of the two NTR cofactor-binding domains, the FAD and the NADPH domains, is not the same. The NADPH domain is rotated by 25° and bent by a 38% closure relative to the FAD domain in comparison with AtNTR-B. The structure may represent an intermediate between the two conformations described previously: the flavin-oxidizing (FO) and the flavin-reducing (FR) conformations. Here, analysis of interdomain contacts as well as phylogenetic studies lead to the proposal of a new reaction scheme in which NTR–Trx interactions mediate the FO to FR transformation.

• OSTI ID: 22347952
• Journal Information: Acta Crystallographica. Section D: Biological Crystallography, Journal Name: Acta Crystallographica. Section D: Biological Crystallography Journal Issue: Pt 9 Vol. 65; ISSN ABCRE6; ISSN 0907-4449
• Country of Publication: Denmark
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
CRYSTAL STRUCTURE
CRYSTALS
ENVIRONMENT
INTERACTIONS
IRON
MOLECULAR WEIGHT
REACTION KINETICS
RESOLUTION
TRANSFORMATIONS