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Updated: Jun 16, 2026

Tracking Single Proteins in Lipid Bilayers Using Fluorescence Microscopy
Published on: December 12, 2025
Higher order structure of aquaporin-4
G P Nicchia1, A Rossi, M G Mola
1Department of General and Environmental Physiology and Centre of Excellence in Comparative Genomics CEGBA, University of Bari, I-70126 Bari, Italy.
Abstract:
Unlike other mammalian AQPs, multiple tetramers of AQP4 associate in the plasma membrane to form peculiar structures called Orthogonal Arrays of Particles (OAPs), that are observable by freeze-fracture electron microscopy (FFEM). However, FFEM cannot give information about the composition of OAPs of different sizes, and due to its technical complexity is not easily applicable as a routine technique. Recently, we employed the 2D gel electrophoresis BN-SDS/PAGE that for the first time enabled the biochemical isolation of AQP4-OAPs from several tissues. We found that AQP4 protein is present in several higher-order complexes (membrane pools of supra-structures) which contain different ratios of M1/M23 isoforms corresponding to AQP4-OAPs of different size. In this paper, we illustrate in detail the potentiality of 2D BN/SDS-PAGE for analyzing AQP4 supra-structures, their relationship with the dystrophin glycoprotein complex and other membrane proteins, and their role as a specific target of Neuromyelitis Optica autoantibodies.
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