Zinc transporter 10 (ZnT10)-dependent extrusion of cellular Mn2+ is driven by an active Ca2+-coupled exchange

Manganese (Mn 2+ ) is extruded from the cell by the zinc transporter 10 (ZnT10). Loss of ZnT10 expression caused by autosomal mutations in the ZnT10 gene leads to hypermanganesemia in multiple organs. Here, combining fluorescent monitoring of cation influx in HEK293-T cells expressing human ZnT10 with molecular modeling of ZnT10 cation selectivity, we show that ZnT10 is exploiting the transmembrane Ca 2+ inward gradient for active cellular exchange of Mn 2+ . In analyzing ZnT10 activity we used the ability of Fura-2 to spectrally distinguish between Mn 2+ and Ca 2+ fluxes. We found that ( a ) application of Mn 2+ -containing Ca 2+ -free solution to ZnT10-expressing cells triggers an influx of Mn 2+ , ( b ) reintroduction of Ca 2+ leads to cellular Mn 2+ extrusion against an inward Mn 2+ gradient, and ( c ) the cellular transport of Mn 2+ by ZnT10 is coupled to a reciprocal movement of Ca 2+ . Remarkably, replacing a single asparagine residue in ZnT10 (Asp-43) with threonine (ZnT10 N43T) converted the Mn 2+ /Ca 2+ exchange to an uncoupled channel mode, permeable to both Ca 2+ and Mn 2+ . The findings in our study identify the first ion transporter that uses the Ca 2+ gradient for active counter-ion exchange. They highlight a remarkable versatility in metal selectivity and mode of transport controlled by the tetrahedral metal transport site of ZnT proteins.