Numerous
membrane-transport proteins are major
drug targets, and therefore a key ingredient in
pharmaceutical development is the availability of reliable, efficient tools for membrane transport characterization and inhibition. Here, we present the use of evanescent-wave sensing for screening of
membrane-protein-mediated transport across
lipid bilayer membranes. This method is based on a direct recording of the temporal variations in the refractive index that occur upon a transfer-dependent change in the solute concentration inside
liposomes associated to a surface plasmon resonance (SPR) active sensor surface. The applicability of the method is demonstrated by a functional study of the
aquaglyceroporin PfAQP from the
malaria parasite Plasmodium falciparum. Assays of the temperature dependence of facilitated diffusion of
sugar alcohols on a single set of PfAQP-reconstituted
liposomes reveal that the activation energies for facilitated diffusion of
xylitol and
sorbitol are the same as that previously measured for
glycerol transport in the
aquaglyceroporin of Escherichia coli (5 kcal/mole). These findings indicate that the
aquaglyceroporin selectivity filter does not discriminate
sugar alcohols based on their length, and that the extra energy cost of
dehydration of larger
sugar alcohols, upon entering the pore, is compensated for by additional hydrogen-bond interactions within the
aquaglyceroporin pore.