The Regulatory Mechanism of Water Permeation by the Selectivity Filter Arginine in Aquaporin Revealed by Solid-State NMR and Computational Analyses

The selectivity filter (SF) of aquaporins (AQPs) governs substrate specificity and permeation efficiency. Despite its functional importance, the mechanistic basis of SF-mediated water transport remains poorly understood, primarily due to the challenge of analyzing the local chemical environment surrounding the SF region. In this study, we employed an integrated approach combining functional measurements, magic-angle spinning solid-state nuclear magnetic resonance (MAS ssNMR) spectroscopy, and computational tools to perform comparative analyses of wild-type and variants of Arg189, a highly conserved residue in the SF region of Escherichia coli aquaporin Z (AqpZ). Our findings reveal that Arg189 plays an indispensable role in stabilizing the hydrogen-bond network and maintaining the proper electrostatic potential distribution along the channel. Specifically, interactions mediated by Arg189 are essential for establishing a continuous, single-file water chain, ensuring efficient water permeation. These results provide atomic-level mechanistic insights into how the SF region fine-tunes the function of AQPs.