Fig. 1.
Role of R262 in substrate uptake by CaiT. (A) Comparison of the Na2 site in LeuT and CaiT. In LeuT, Na2 is coordinated by sidechains as well as backbone carbonyl interactions from TM1 and TM8, whereas in CaiT the Na2 position is occupied by R262 with similar hydrogen bond interactions to TM1′ and TM8′. (B) l-carnitine uptake by PmCaiT wild-type and R262 mutants. Proteoliposomes were preloaded with 10 mM cold γ-butyrobetaine, and counterflow uptake activity of 40 μM [14C] l-carnitine was measured. All data points are the averages of three independent experiments, with error bars indicating the SD of the measurements.