Structural and functional properties of a plant NRAMP related aluminum transporter

The transport of transition metal ions by members of the SLC11/NRAMP family constitutes a ubiquitous mechanism for the uptake of Fe ²⁺ and Mn ²⁺ across all kingdoms of life. Despite the strong conservation of the family, two of its branches have evolved a distinct substrate preference with one mediating Mg ²⁺ uptake in prokaryotes and another the transport of Al ³⁺ into plant cells. Our previous work on the SLC11 transporter from Eggerthella lenta revealed the basis for its Mg ²⁺ selectivity (Ramanadane et al., 2022). Here we have addressed the structural and functional properties of a putative Al ³⁺ transporter from Setaria italica. We show that the protein transports diverse divalent metal ions and binds the trivalent ions Al ³⁺ and Ga ³⁺ , which are both presumable substrates. Its cryo-EM structure displays an occluded conformation that is closer to an inward-than an outward-facing state with a binding site that is remodeled to accommodate the increased charge density of its transported substrate.