Figure 4.

Cation dependence of fluoride transport by Fluc-R22K. A. R22 coordination. Coloring as in Figure 1. Yellow subunit is shown in ribbon format for clarity, except for T73 main chain atoms, which are shown as sticks. Residues within coordination distance of the central cation or within H-bonding distance of R22 are labeled. R22 and T81 sidechain, and G77-T80 main chain atoms are shown as sticks. B. Fluoride efflux from Bpe-R22K proteoliposomes incubated for 12 hours with 10 mM Na⁺, NMG⁺, or Li⁺ isethionate. Efflux monitored with a fluoride-specific electrode.