Characterization of Aquaporin Z proteoliposome structure and functionality via microscopy and scattering methods

Aquaporins are known for their efficient water transport capabilities and have been widely studied in the past decades. However, creating a biomimetic system mirroring natural water filtration processes still poses a challenge related to performance and stability. To study the protein reconstitution and functionality, this work presents an analytical toolkit using the model system of AqpZ reconstituted phosphatidylcholine proteoliposomes. Combining findings from dynamic light scattering, cryogenic transmission electron microscopy, laser scanning confocal microscopy, stimulated emission depletion microscopy, stopped flow-light scattering and small-angle X-ray scattering provides an assessment of structural and functional characteristics of AqpZ embedding in the bilayer of liposomes. Findings of this work reveal that the incorporation of AqpZ into liposomes promotes an increase within the hydrophobic bilayer thickness as well as within the overall size of the vesicles. AqpZ, AqpZ-GFP and AqpZ-Atto594 are studied and show distinct permeability profiles. Despite all three displaying a successful structural reconstitution into the liposomes, labeled protein variants demonstrate a loss of function. A series of protein concentrations are utilized to extract quantitative information regarding the reconstitution process, revealing constant water transport per AqpZ and thus a consistent trend of increased reconstitution and permeability as a function of AqpZ concentration, as determined by stopped flow-light scattering and detailed further via global fitting of small-angle X-ray scattering data.