title: Molecular basis of nitrate uptake by the plant nitrate transporter NRT1.1.
abstract: The NRT1/PTR family of proton-coupled transporters are responsible for nitrogen assimilation in eukaryotes and bacteria through the uptake of peptides. However, in most plant species members of this family have evolved to transport nitrate as well as additional secondary metabolites and hormones. In response to falling nitrate levels, NRT1.1 is phosphorylated on an intracellular threonine that switches the transporter from a low-affinity to high-affinity state. Here we present both the apo and nitrate-bound crystal structures of Arabidopsis thaliana NRT1.1, which together with in vitro binding and transport data identify a key role for His 356 in nitrate binding. Our data support a model whereby phosphorylation increases structural flexibility and in turn the rate of transport. Comparison with peptide transporters further reveals how the NRT1/PTR family has evolved to recognize diverse nitrogenous ligands, while maintaining elements of a conserved coupling mechanism within this superfamily of nutrient transporters.
authors.affiliation: Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK.
authors.forename: Joanne L
authors.initials: JL
authors.lastname: Parker
authors.affiliation: 1] Department of Biochemistry, University of Oxford, Oxford OX1 3QU, UK [2] Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot OX11 0FA, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Newstead
mesh_terms: D027321:Anion Transport Proteins / Q000737:chemistry* / Q000378:metabolism*; D017360:Arabidopsis / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D006639:Histidine / Q000737:chemistry / Q000378:metabolism; D017136:Ion Transport; D008958:Models, Molecular; D000091285:Nitrate Transporters; D009566:Nitrates / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D011522:Protons; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D027321:Anion Transport Proteins; C101492:NRT1.1 protein, Arabidopsis; D000091285:Nitrate Transporters; D009566:Nitrates; D010940:Plant Proteins; D011522:Protons; D010769:Phosphothreonine; D006639:Histidine