Untersuchung der Kationenfiltermechanismen in Aquaporin-1
In the present work, the role of two highly conserved constrictions (ar/R-region and NPA-region) in Aquaporin-1 (AQP1) cation exclusion mechanism is described by mutational analysis of rat AQP1. New mutations in the NPA-region were characterized and combined with mutations in the ar/R-region previously shown to cause proton leaks. Permeability for protons, (methyl-) ammonium, potassium and sodium was tested using phenotypic Saccharomyces cerevsiae growth assays. Measurements for permeability of water, urea and glycerol were performed in Xenopus laevis oocyte swelling assays. Asparagine to aspartate exchange in the NPA-region caused a sodium leak. Combined mutations in both regions showed permeability for H+, Na+, K+ and NH4+; water permeability was decreased by 80%. It was shown that cation exclusion in AQP1 is a synergistic process of both constrictions whereby the NPA region filters K+ and Na+ as well as H+ to a certain extent and the ar/R-region completes the proton filtration.