Open AccessStructure of Hordeum vulgare NADPH‐dependent thioredoxin reductase 2. Unwinding the reaction mechanism
Author(s) -
Kirkensgaard Kristine G.,
Hägglund Per,
Finnie Christine,
Svensson Birte,
Henriksen Anette
Publication year - 2009
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s0907444909021817
Subject(s) - hordeum vulgare , thioredoxin , flavin group , cofactor , arabidopsis thaliana , flavin adenine dinucleotide , stereochemistry , chemistry , biochemistry , oxidoreductase , biology , enzyme , botany , gene , poaceae , mutant
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, Hv NTR2 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 cryst of 19.0% and an R free of 23.8%. The dimeric protein is structurally similar to the structures of At NTR‐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 At NTR‐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.