Scattering versus fluorescence self-quenching: more than a question of faith for the quantification of water flux in large unilamellar vesicles?

Abstract

The endeavors to understand the determinants of water permeation through membrane channels, the effect of the lipid or polymer membrane on channel function, the development of specific water flow inhibitors,...

Modeling of SGLT1 in Reconstituted Systems Reveals Apparent Ion-Dependencies of Glucose Uptake and Strengthens the Notion of Water-Permeable Apo States

“…Our vesicle model is unique in that it incorporates a solute carrier. Yet, other vesicle models exist, which account for passive diffusion of water ( Wachlmayr et al, 2022 ), weak acids ( Hannesschlaeger et al, 2019a ; Gabba and Poolman, 2020 ), and ions ( Megens et al, 2014 ; Shen et al, 2020 ) through the vesicular membrane. However, due to their different scopes, none of them simultaneously modeled 1) membrane potential ( Gabba and Poolman, 2020 ), 2) partial volume effects ( Hannesschlaeger et al, 2019b ; Gabba and Poolman, 2020 ; Shen et al, 2020 ), 3) de/protonation of the buffer ( Gabba and Poolman, 2020 ; Shen et al, 2020 ), and 4) self-dissociation of water ( Gabba and Poolman, 2020 ).…”

“…However, due to their different scopes, none of them simultaneously modeled 1) membrane potential ( Gabba and Poolman, 2020 ), 2) partial volume effects ( Hannesschlaeger et al, 2019b ; Gabba and Poolman, 2020 ; Shen et al, 2020 ), 3) de/protonation of the buffer ( Gabba and Poolman, 2020 ; Shen et al, 2020 ), and 4) self-dissociation of water ( Gabba and Poolman, 2020 ). While we modeled all of the above, we disregarded the size distribution of the vesicle ensemble as was included in models, which dealt with water ( Wachlmayr et al, 2022 ) and weak acid permeation ( Gabba and Poolman, 2020 ).…”

“…To improve the model, its predictions must be tested in experiments. A readily accessible parameter, for instance, is the time course of volume change via scattering or fluorescence self-quenching experiments ( Wachlmayr et al, 2022 ). The latter is performed via intra luminal trapped fluorophores as volume readout.…”

The hidden intricacies of aquaporins: Remarkable details in a common structural scaffold

“…Quantitative unitary water permeabilities pf of AQPs, summarized in Figure 1, are rare and span almost one order of magnitude. Currently, diverse methods are used to obtain pf, delivering sometimes more and sometimes less coherent results (74)(75)(76)(77)(78). Only recently, driven by methodological advancements (4,76,79,80), the major determinants of single-file transport of water through membrane channels were found to be the number of H-bonds water molecules form with pore lining residues (4), positive charges at the pore mouth (81), channel gating (77) and potentially the shape of the vestibule (82).…”

The Hidden Intricacies of Aquaporins: Remarkable Details in a Common Structural Scaffold

“…Currently, diverse methods are used to obtain p f , delivering sometimes more and sometimes less coherent results. [72][73][74][75][76] Only recently, driven by methodological advancements, [3,74,[76][77][78] the major determinants of single-file transport of water through membrane channels were found to be the number of H-bonds water molecules form with pore-lining residues, [3] positive charges at the pore mouth, [79] channel gating, [75] and potentially the shape of the vestibule. [80] Thereby, high p f is intricately linked to a low activation energy of water transport.…”