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 fromEggerthella lentarevealed the basis for its Mg2+selectivity (Ramanadane et al., 2022). Here we have addressed the structural and functional properties of a putative Al3+transporter fromSetaria italica. 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-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.