Structural Superimposition

Abstact

Membrane transporters and channels are generally assumed to be based on distinct structural and functional principles. SLC26A11, a solute carrier with high expression levels in the brain, has been proposed to function as either an anion transporter or a channel. Here, we resolve this apparent discrepancy by demonstrating that SLC26A11 is a dual-function protein capable of operating as both a sulfate transporter and a chloride channel. By resolving its structure and combining biochemical studies and molecular dynamics simulations, we show that SLC26A11 exhibits all the hallmarks of a secondary transporter. The mechanistic basis for its selective ion transport identifies the protein as the elusive lysosomal sulfate exporter. Additionally, we demonstrate that SLC26A11 exhibits an uncoupled, channel-like chloride conductance gated by proton:sulfate symport. Our finding that the chloride-conducting state arises from the transport cycle may contribute to the development of therapeutic strategies for treating brain edema, and the identification of its role in lysosome sulfate efflux may provide new approaches to study and treat lysosomal storage diseases.