(C) A cartoon of the central channel formed within a PfFNT protomer. The channel contains one constriction site in this conformational state. Residues forming the constriction and the K35-D103-N108 and K177-E229-N234 triads are illustrated as sticks. Residues F94, I97 and L104, which form the first constriction site in the apo-PfFNT structure, is also included in the figure. 