Aquaporins are highly selective water channel proteins integrated into plasma membranes of single cell organisms; plant roots and stromae; eye lenses， renal and red blood cells in vertebrates. To date， only a few microbial aquaporins have been characterized and their physiological importance is not well understood. Here we report on the cloning， expression and characterization of a novel aquaporin， RsAqpZ， from a purple photosynthetic bacterium， Rhodobacter sphaeroides ATCC 17023. The protein was expressed homologously at a high yield (∼20 mg/L culture) under anaerobic photoheterotrophic growth conditions. Stopped-flow light scattering experiments demonstrated its high water permeability (0.17±0.... More
Aquaporins are highly selective water channel proteins integrated into plasma membranes of single cell organisms; plant roots and stromae; eye lenses， renal and red blood cells in vertebrates. To date， only a few microbial aquaporins have been characterized and their physiological importance is not well understood. Here we report on the cloning， expression and characterization of a novel aquaporin， RsAqpZ， from a purple photosynthetic bacterium， Rhodobacter sphaeroides ATCC 17023. The protein was expressed homologously at a high yield (∼20 mg/L culture) under anaerobic photoheterotrophic growth conditions. Stopped-flow light scattering experiments demonstrated its high water permeability (0.17±0.05 cm/s) and low energy of activation for water transport (2.93±0.60 kcal/mol) in reconstituted proteoliposomes at a protein to lipid ratio (w/w) of 0.04. We developed a fluorescence correlation spectroscopy based technique and utilized a fluorescent protein fusion of RsAqpZ， to estimate the single channel water permeability of RsAqpZ as 1.24 (±0.41) x 10(-12) cm(3)/s or 4.17 (±1.38)×10(10) H2O molecules/s， which is among the highest single channel permeability reported for aquaporins. Towards application to water purification technologies， we also demonstrated functional incorporation of RsAqpZ in amphiphilic block copolymer membranes.
