Extended Data Fig. 9: Superposition of phosphate molecule in Site 1 and the current model for alternating access transport in Oat1.
From: Molecular basis for selective uptake and elimination of organic anions in the kidney by OAT1
a, Superposition of αKG and phosphate bound Oat1 (r.m.s.d. 0.633 Å over 496 Cα atoms). Inset left, zoomed in view of Site 1 with key residues labelled. b, (i) The inward open state of OAT1 is stabilised through the formation of the salt bridge between Asp378 (TM8) and Lys431 (TM10). (ii) α-KG binding to Site 1 results in the breakage of the Asp378-Lys431 salt bridge, enabling the transporter to switch to the outward open state. (iii) The outward open state is stabilised through the interactions between the ‘+−+’ motifs on TMs 4,5 and 10,11. (iv) Binding of organic anions to Site 1 or drugs to Site 3 stabilise the C-terminal domains and facilitate reorientation back to the inward open state, where the ligand is released into the cell. The chloride ion (green circle) in Site 2 facilitates transport by rigidifying the C-terminal bundle and may contribute to positioning α-KG in Site 1 and drugs into Site 3. (v) Probenecid inhibits OAT1 by interfering with the Asp378-Lys431 salt bridge lock, binding the extracellular gate residues (Asn35 & Tyr354) and may also disrupt Cl− ion binding. c, Analysis of the electrostatic surface potential of the binding site in Oat1. The N-terminal bundle contains positively charged regions that lead into the main cavity from the extracellular and intracellular sides of the membrane respectively. These will facilitate anion entry and exit. However, the surfaces adjacent to Sites 1, 2 and 3 are notable for being hydrophobic and biochemically inert.
