title: A new gating site in human aquaporin-4: Insights from molecular dynamics simulations.
abstract: Aquaporin-4 (AQP4) is the predominant water channel in different organs and tissues. An alteration of its physiological functioning is responsible for several disorders of water regulation and, thus, is considered an attractive target with a promising therapeutic and diagnostic potential. Molecular dynamics (MD) simulations performed on the AQP4 tetramer embedded in a bilayer of lipid molecules allowed us to analyze the role of spontaneous fluctuations occurring inside the pore. Following the approach by Hashido et al. [Hashido M, Kidera A, Ikeguchi M (2007) Biophys J 93: 373-385], our analysis on 200ns trajectory discloses three domains inside the pore as key elements for water permeation. Herein, we describe the gating mechanism associated with the well-known selectivity filter on the extracellular side of the pore and the crucial regulation ensured by the NPA motifs (asparagine, proline, alanine). Notably, on the cytoplasmic side, we find a putative gate formed by two residues, namely, a cysteine belonging to the loop D (C178) and a histidine from loop B (H95). We observed that the spontaneous reorientation of the imidazole ring of H95 acts as a molecular switch enabling H-bond interaction with C178. The occurrence of such local interaction seems to be responsible for the narrowing of the pore and thus of a remarkable decrease in water flux rate. Our results are in agreement with recent experimental observations and may represent a promising starting point to pave the way for the discovery of chemical modulators of AQP4 water permeability.
authors.affiliation: Dipartimento Interateneo di Fisica "M. Merlin," Università di Bari "Aldo Moro," INFN, Via E. Orabona, 4, Bari I-70126, Italy; Centro Ricerche TIRES, University of Bari "Aldo Moro," Via Amendola 173, Bari I-70126, Italy.
authors.forename: Domenico
authors.initials: D
authors.lastname: Alberga
authors.affiliation: Dipartimento di Farmacia, Scienze del Farmaco, Università di Bari "Aldo Moro," Via Orabona 4, Bari 70126, Italy; Centro Ricerche TIRES, University of Bari "Aldo Moro," Via Amendola 173, Bari I-70126, Italy.
authors.forename: Orazio
authors.initials: O
authors.lastname: Nicolotti
authors.affiliation: Dipartimento Interateneo di Fisica "M. Merlin," Università di Bari "Aldo Moro," INFN, Via E. Orabona, 4, Bari I-70126, Italy; Centro Ricerche TIRES, University of Bari "Aldo Moro," Via Amendola 173, Bari I-70126, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Lattanzi
authors.affiliation: Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," Bari 70126, Italy.
authors.forename: Grazia Paola
authors.initials: GP
authors.lastname: Nicchia
authors.affiliation: Department of Bioscience, Biotechnologies and Biopharmaceutics and Center of Excellence in Comparative Genomics, University of Bari "Aldo Moro," Bari 70126, Italy.
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," Bari 70126, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Pisani
authors.affiliation: Consiglio Nazionale delle Ricerche (CNR), Istituto per la Sintesi Organica e la Fotoreattività (ISOF), Via Gobetti 101, Bologna 40129, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Benfenati
authors.affiliation: Dipartimento di Farmacia, Scienze del Farmaco, Università di Bari "Aldo Moro," Via Orabona 4, Bari 70126, Italy. Electronic address: giuseppe.mangiatordi@uniba.it.
authors.forename: Giuseppe Felice
authors.initials: GF
authors.lastname: Mangiatordi
keywords: AQP4; Aquaporins; Gating; Molecular dynamics; Water transport