Structural and functional properties of a plant NRAMP-related aluminum transporter.

Abstract

The transport of transition metal ions by members of the SLC11/NRAMP family constitutes a ubiquitous mechanism for the uptake of Fe²⁺ and Mn²⁺ 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 Mg²⁺ uptake in prokaryotes and another the transport of Al³⁺ into plant cells. Our previous work on the SLC11 transporter from <i>Eggerthella lenta</i> revealed the basis for its Mg²⁺ selectivity (Ramanadane et al., 2022). Here, we have addressed the structural and functional properties of a putative Al³⁺ transporter from <i>Setaria italica</i>. We show that the protein transports diverse divalent metal ions and binds the trivalent ions Al³⁺ and Ga³⁺, which are both presumable substrates. Its cryo-electron microscopy (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.