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Pisani F, Simone L, Mola MG, De Bellis M, Mastrapasqua M, Ruggieri M, Trojano M, Nicchia GP, Svelto M, Frigeri A. Host-Cell Type Dependent Features of Recombinant Human Aquaporin-4 Orthogonal Arrays of Particles-New Insights for Structural and Functional Studies. Cells 2019; 8:cells8020119. [PMID: 30717425 PMCID: PMC6406603 DOI: 10.3390/cells8020119] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Revised: 01/26/2019] [Accepted: 02/01/2019] [Indexed: 11/16/2022] Open
Abstract
The CNS plasma-membrane water channel aquaporin-4 (AQP4) is expressed as two major isoforms able to aggregate into supramolecular assemblies known as ‘orthogonal arrays of particles’ (OAPs). OAP subnanometric features are largely unknown mainly because a method for the expression, isolation, and crystallization of integral human OAPs has not been developed. Here, the human OAP-forming isoform M23-AQP4 was expressed in insect and mammalian cell lines and AQP4 and OAP features evaluated. Native size exclusion chromatography was employed to isolate and analyze authentically folded OAPs, and neuromyelitis optica (NMO)-specific sandwich ELISA was developed to test OAP-integrity. The results demonstrate that in insect cells most AQP4 remains intracellular and unfolded and that OAPs are largely disassembled after the detergent extraction step. In mammalian cells, AQP4 showed regular plasma membrane targeting and OAPs exhibited strong post-extraction stability. Starting from the mammalian cell expression system, we isolated authentically folded OAPs. Together these data suggest a new strategy for expressing and isolating integral recombinant human OAPs and providing new insights into the cell-type dependent OAP-assembly and post-extraction stability, potentially useful to design new approaches for structural and functional studies of OAP and for other plasma membrane proteins organized into supramolecular structures.
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Affiliation(s)
- Francesco Pisani
- Department of Bioscience, Biotechnologies and Biopharmaceutic, Univ. of Bari "Aldo Moro", 70124 Bari, Italy.
| | - Laura Simone
- Fondazione IRCCS Casa Sollievo della Sofferenza, Cancer Stem Cells Unit, 71013 San Giovanni Rotondo (FG), Italy.
| | - Maria Grazia Mola
- Department of Bioscience, Biotechnologies and Biopharmaceutic, Univ. of Bari "Aldo Moro", 70124 Bari, Italy.
| | - Manuela De Bellis
- Department of Bioscience, Biotechnologies and Biopharmaceutic, Univ. of Bari "Aldo Moro", 70124 Bari, Italy.
| | - Maria Mastrapasqua
- School of Medicine, Basic Medical Sciences, Neuroscience and Sense Organs, Univ. of Bari "Aldo Moro", 70124 Bari, Italy.
| | - Maddalena Ruggieri
- School of Medicine, Basic Medical Sciences, Neuroscience and Sense Organs, Univ. of Bari "Aldo Moro", 70124 Bari, Italy.
| | - Maria Trojano
- School of Medicine, Basic Medical Sciences, Neuroscience and Sense Organs, Univ. of Bari "Aldo Moro", 70124 Bari, Italy.
| | - Grazia Paola Nicchia
- Department of Bioscience, Biotechnologies and Biopharmaceutic, Univ. of Bari "Aldo Moro", 70124 Bari, Italy.
| | - Maria Svelto
- Department of Bioscience, Biotechnologies and Biopharmaceutic, Univ. of Bari "Aldo Moro", 70124 Bari, Italy.
- Institute of Biomembranes, Bioenergetics and Molecular Biotechnologies, National Research Council, 70126 Bari, Italy.
| | - Antonio Frigeri
- School of Medicine, Basic Medical Sciences, Neuroscience and Sense Organs, Univ. of Bari "Aldo Moro", 70124 Bari, Italy.
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Comparative molecular dynamics study of neuromyelitis optica-immunoglobulin G binding to aquaporin-4 extracellular domains. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:1326-1334. [PMID: 28477975 DOI: 10.1016/j.bbamem.2017.05.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Revised: 04/27/2017] [Accepted: 05/02/2017] [Indexed: 01/26/2023]
Abstract
Neuromyelitis optica (NMO) is an inflammatory demyelinating disease of the central nervous system in which most patients have serum autoantibodies (called NMO-IgG) that bind to astrocyte water channel aquaporin-4 (AQP4). A potential therapeutic strategy in NMO is to block the interaction of NMO-IgG with AQP4. Building on recent observation that some single-point and compound mutations of the AQP4 extracellular loop C prevent NMO-IgG binding, we carried out comparative Molecular Dynamics (MD) investigations on three AQP4 mutants, TP137-138AA, N153Q and V150G, whose 295-ns long trajectories were compared to that of wild type human AQP4. A robust conclusion of our modeling is that loop C mutations affect the conformation of neighboring extracellular loop A, thereby interfering with NMO-IgG binding. Analysis of individual mutations suggested specific hydrogen bonding and other molecular interactions involved in AQP4-IgG binding to AQP4.
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