The SLC34 family of Na+-driven Pi transporters are indispensable gatekeepers of the body’s phosphate supply, ensuring that cells, tissues, and organs receive the Pi essential for growth, energy production, and signaling.
We determined the first structures of an SLC34 family member, revealing a unique fold and the structural basis of transport. Our extensive complementary structure-function studies yield important insight into substrate and ion recognition, the role of Na+, coupling between ions and substrate, and critical SLC34 domains for the transport cycle. Our findings indicate that SLC34 transporters utilize an unexpected alternating access mechanism in which substantial conformational changes are confined to a peripheral gate domain, with the transport domain, where ions and substrates bind, remaining comparatively stationary.