Molecular Basis of Prostaglandin E2 Reuptake by Organic Anion Transporter PGT

Prostaglandins (PGs) are bioactive lipids that regulate inflammation, reproduction, and vasopermeability. Timely clearance of excessive PGs is critical to prevent potential damages caused by prolonged signalling. The high-affinity prostaglandin transporter (PGT) plays an essential role in this termination process by efficiently re-uptaking PGs into cells. Here, we report human PGT structures in different oligomerization and substrate-binding states. Beyond the canonical MFS-fold, PGT harbours a unique cystine-rich extracellular segment that incorporates a Kazal-like domain crucial for PGT localization and activity. Two distinct PGE2-bound structures revealed essential elements for substrate recognition, elucidating a PGE2-flipping process during the multi-stop translocation cycle. Notably, PGT dimerizes in detergent micelles and lipid nanodiscs. This dimerization drastically increases the mobility of the extracellular region and induces a profound rotation of the C-domain transmembrane helices, an unprecedented observation for MFS transporters. These functionally distinct snapshots thus shed light on prostaglandin clearance and reveal uncommon features of MFS transporters.