Point Mutation of Aquaporin 4 Impairs its Binding in Neuromyelitis Optica

Aquaporin 4 (AQP4) is the principal aquaporin expressed in astrocytes throughout the central nervous system. An autoantibody, IgG, that binds to AQP4 leads to a rare disease called neuromyelitis optica (NMO), which is characterized by paralysis and loss of vision. Current treatments for NMO are few and involve non‐specific immunosuppression. The Summit Country Day School MSOE Center for BioMolecular Modeling MAPS Team used 3D modeling and printing technology to examine structure‐function relationships of the AQP4 epitope for NMO‐IgG. Understanding the molecular structure of the AQP4 epitope is an important step in explaining its binding to NMO‐IgG. NMO‐IgG primarily interacts with the accessible AQP4 extracellular loops A, C, and E. These loops change their conformation when AQP4 arrange into orthogonal arrays of particles, thus enabling attachment of NMO‐IgG and facilitating complement binding. Studies on the point mutation of aspartate in position 69 (D69) revealed conformational changes such as 1) reorientation of threonine in position 62, 2) weakened hydrogen bond interaction between leucine in position 53 and threonine in position 56, 3) increased mobility of loop A, and 4) disruption of epitope reorganization of AQP4. Overall, D69 substitution and the subsequent conformational changes in loop A leads to impairment of binding between AQP4 and the NMO‐IgG. Determining the role of extracellular loop A between and within AQP4 monomers will aid in understanding how it contributes to antigen recognition. Prevention of the binding of AQP4 by NMO‐IgG is an important strategy for developing targeted therapy in NMO. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .