title: Identification of a point mutation impairing the binding between aquaporin-4 and neuromyelitis optica autoantibodies.
abstract: Neuromyelitis optica (NMO) is characterized by the presence of pathogenic autoantibodies (NMO-IgGs) against supra-molecular assemblies of aquaporin-4 (AQP4), known as orthogonal array of particles (OAPs). NMO-IgGs have a polyclonal origin and recognize different conformational epitopes involving extracellular AQP4 loops A, C, and E. Here we hypothesize a pivotal role for AQP4 transmembrane regions (TMs) in epitope assembly. On the basis of multialignment analysis, mutagenesis, NMO-IgG binding, and cytotoxicity assay, we have disclosed the key role of aspartate 69 (Asp(69)) of TM2 for NMO-IgG epitope assembly. Mutation of Asp(69) to histidine severely impairs NMO-IgG binding for 85.7% of the NMO patient sera analyzed here. Although Blue Native-PAGE, total internal reflection fluorescence microscopy, and water transport assays indicate that the OAP Asp(69) mutant is similar in structure and function to the wild type, molecular dynamic simulations have revealed that the D(69)H mutation has the effect of altering the structural rearrangements of extracellular loop A. In conclusion, Asp(69) is crucial for the spatial control of loop A, the particular molecular conformation of which enables the assembly of NMO-IgG epitopes. These findings provide additional clues for new strategies for NMO treatment and a wealth of information to better approach NMO pathogenesis.
authors.affiliation: Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," 70126 Bari.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pisani
authors.affiliation: Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," 70126 Bari.
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Mola
authors.affiliation: Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," 70126 Bari.
authors.forename: Laura
authors.initials: L
authors.lastname: Simone
authors.affiliation: Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," 70126 Bari.
authors.forename: Stefania
authors.initials: S
authors.lastname: Rosito
authors.affiliation: Dipartimento Interateneo di Fisica "M. Merlin", INFN and TIRES, Università di Bari "Aldo Moro", via Orabona, 4, 70126 Bari, Italy.
authors.forename: Domenico
authors.initials: D
authors.lastname: Alberga
authors.affiliation: Dipartimento di Farmacia-Scienze del Farmaco, Via Orabona, 4, Università di Bari "Aldo Moro", Bari, 70126 Bari, and.
authors.forename: Giuseppe Felice
authors.initials: GF
authors.lastname: Mangiatordi
authors.affiliation: Dipartimento Interateneo di Fisica "M. Merlin", INFN and TIRES, Università di Bari "Aldo Moro", via Orabona, 4, 70126 Bari, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Lattanzi
authors.affiliation: Dipartimento di Farmacia-Scienze del Farmaco, Via Orabona, 4, Università di Bari "Aldo Moro", Bari, 70126 Bari, and.
authors.forename: Orazio
authors.initials: O
authors.lastname: Nicolotti
authors.affiliation: Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," 70126 Bari.
authors.forename: Antonio
authors.initials: A
authors.lastname: Frigeri
authors.affiliation: Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," 70126 Bari.
authors.forename: Maria
authors.initials: M
authors.lastname: Svelto
authors.affiliation: Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," 70126 Bari,. Electronic address: graziapaola.nicchia@uniba.it.
authors.forename: Grazia Paola
authors.initials: GP
authors.lastname: Nicchia
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D051401:Aquaporin 4 / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D001323:Autoantibodies / Q000378:metabolism*; D001692:Biological Transport; D000939:Epitopes / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007074:Immunoglobulin G / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D009471:Neuromyelitis Optica / Q000097:blood / Q000276:immunology*; D017354:Point Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D014867:Water / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: C496030:AQP4 protein, human; D051401:Aquaporin 4; D001323:Autoantibodies; D000939:Epitopes; D007074:Immunoglobulin G; D014867:Water
keywords: Aquaporin; Aquaporin-4; Astrocyte; Autoimmune Disease; Epitope Determinant; Epitope Mapping; NMO-IgG; Neurodegenerative Disease; Neuromyelitis Optica; Orthogonal Array of Particles