Structure and function of the divalent anion/Na(+) symporter from Vibrio cholerae and a humanized variant

Integral membrane proteins of the divalent anion/Na(+) symporter (DASS) family translocate dicarboxylate, tricarboxylate or sulphate across cell membranes, typically by utilizing the preexisting Na(+) gradient. The molecular determinants for substrate recognition by DASS remain obscure, largely owing to the absence of any substrate-bound DASS structure. Here we present 2.8-Å resolution X-ray structures of VcINDY, a DASS from Vibrio cholerae that catalyses the co-transport of Na(+) and succinate. These structures portray the Na(+)-bound VcINDY in complexes with succinate and citrate, elucidating the binding sites for substrate and two Na(+) ions. Furthermore, we report the structures of a humanized variant of VcINDY in complexes with succinate and citrate, which predict how a human citrate-transporting DASS may interact with its bound substrate. Our findings provide insights into metabolite transport by DASS, establishing a molecular basis for future studies on the regulation of this transport process.