Crystal structure of the plant dual-affinity nitrate transporter NRT1.1.

ABSTRACT: Nitrate is a primary nutrient for plant growth, but its levels in soil can fluctuate by several orders of magnitude. Previous studies have identified Arabidopsis NRT1.1 as a dual-affinity nitrate transporter that can take up nitrate over a wide range of concentrations. The mode of action of NRT1.1 is controlled by phosphorylation of a key residue, Thr?101; however, how this post-translational modification switches the transporter between two affinity states remains unclear. Here we report the crystal structure of unphosphorylated NRT1.1, which reveals an unexpected homodimer in the inward-facing conformation. In this low-affinity state, the Thr?101 phosphorylation site is embedded in a pocket immediately adjacent to the dimer interface, linking the phosphorylation status of the transporter to its oligomeric state. Using a cell-based fluorescence resonance energy transfer assay, we show that functional NRT1.1 dimerizes in the cell membrane and that the phosphomimetic mutation of Thr?101 converts the protein into a monophasic high-affinity transporter by structurally decoupling the dimer. Together with analyses of the substrate transport tunnel, our results establish a phosphorylation-controlled dimerization switch that allows NRT1.1 to uptake nitrate with two distinct affinity modes.

SUBMITTER: Sun J 

PROVIDER: S-EPMC3968801 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature