MocoMojo: Crystal Structure Reveals Essential Features of Eukaryotic Assimilatory Nitrate Reduction

The assimilatory nitrate reduction pathway is a vital biological process, as it is one of the principal routes by which inorganic nitrogen is incorporated into organic compounds in higher plants, algae, and fungi. After uptake into cells by nitrate transporters, the first and rate-limiting step in this pathway is the reduction of nitrate to nitrite catalyzed by NAD(P)H:nitrate reductase (NR), a molybdenum cofactor (Moco) enzyme that is highly regulated both at the transcriptional and posttranslational level. An understanding of NR mechanism of action and regulation is of fundamental importance in plant biology and in addition has implications for the control of nitrogen pollution. Nitrate accumulation in surface and groundwater is of concern in many areas of the world because it poses human health threats and is a major contributor to eutrophication of lakes and streams. Basic research on eukaryotic NR may lead to the development of genetically engineered crops with increased nitrate use efficiency, leading to improved crop yields and reducing the need for application of nitrogen fertilizers (Campbell, 1999). Interestingly, recombinant NR also has been developed as an effective and environmentally safe alternative to heavy metal–based assays for nitrate testing (Patton et al., 2002).