8.A.20 The Plant/Algal/Chlorella Nitrate Transporter Accessory Protein (NAR2.1) Family
AtNRT2.1 is a component of a plasma membrane, Arabidopsis thaliana, two-component, inducible, high-affinity, nitrate transport system. Yong et al. (2010) used immunological and transient protoplast expression methods to demonstrate that an intact two-component complex of AtNRT2.1 and AtNAR2.1 (AtNRT3.1) is localized in the plasma membrane. A. thaliana mutants lacking AtNAR2.1 exhibit extremely poor growth on low nitrate as the sole source of nitrogen. Using anti-NRT2.1 antibodies, a purified oligomeric polypeptide (approximate molecular mass 150kDa) was identified, but monomeric AtNRT2.1 was absent. This oligomer was also observed in the wild-type, and was resolved, using SDS-PAGE for the second dimension, into two polypeptides with molecular masses of approximately 48 and 26kDa, corresponding to AtNRT2.1 and myc-tagged AtNAR2.1, respectively. The oligomer was absent from NRT2.1 or NAR2.1 mutants, suggesting that this complex is the active nitrate transporter. The molecular mass of the intact oligomer suggests that the functional unit for high-affinity nitrate influx may be a tetramer consisting of two subunits each of AtNRT2.1 and AtNAR2.1. NAR2 has two putative TMSs at its N- and C- termini. The Chlorella protein is shorter and lacks the N-terminal TMS.
WR3; wound responsive protein-3 or NAR2.1, an accessory protein for transport via 2.A.1.8.12 (Yong et al., 2010). May act as a dual component transporter with NTR2.1; required for high-affinity nitrate transport. Acts as a repressor of lateral root initiation. May be involved in targeting NRT2 proteins to the plasma membrane.
WR3 of Arabidopsis thaliana (Q9FGS5)
High-affinity sodium-dependent nitrate transporter accessory protein, NAR2, of 210 aas and 2 TMSs, one N-terminal and one C-terminal (Rubio et al. 2019). It functions with NO3- transporter with TC# 2.A.1.8.18.
NAR2 of Zostera marina
Homologue of NAR2.1
NAR2.1 homologue of Chlamydomonas reinhardtii (A8J4P7)
Homologue of NAR2.1 (210aas)
NAR2.1 homologue of Chlorella variabilis (E1ZNI7)