Proton-coupled folate transporter
folate import across plasma membrane
Structural basis of antifolate recognition and transport by PCFT.
Folates (also known as vitamin B9) have a critical role in cellular metabolism as the starting point in the synthesis of nucleic acids, amino acids and the universal methylating agent S-adenylsmethionine<sup>1,2</sup>. Folate deficiency is associated with a number of developmental, immune and neurological disorders<sup>3-5</sup>. Mammals cannot synthesize folates de novo; several systems have therefore evolved to take up folates from the diet and distribute them within the body<sup>3,6</sup>. The proton-coupled folate transporter (PCFT) (also known as SLC46A1) mediates folate uptake across the intestinal brush border membrane and the choroid plexus<sup>4,7</sup>, and is an important route for the delivery of antifolate drugs in cancer chemotherapy<sup>8-10</sup>. How PCFT recognizes folates or antifolate agents is currently unclear. Here we present cryo-electron microscopy structures of PCFT in a substrate-free state and in complex with a new-generation antifolate drug (pemetrexed). Our results provide a structural basis for understanding antifolate recognition and provide insights into the pH-regulated mechanism of folate transport mediated by PCFT.