AQP4 and neuromyelitis optica: Taken together, the data here presented show that the expression of M23-AQP4 in mammalian cells and OAP enrichment by nSEC are mandatory to obtain integral human AQP4-OAPs for downstream applications such as structural and functional studies, crystallography, molecular docking, small molecule inhibitor screening, domain binding property studies, and OAPs-based NMO diagnostic applications.