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Cells 2018, 7(11), 209; https://doi.org/10.3390/cells7110209

Aquaporins: More Than Functional Monomers in a Tetrameric Arrangement

1
Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EGA, Argentina
2
Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires C1428EGA CABA, Argentina
3
Instituto de investigaciones Médicas A. Lanari, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires C1427ARO, Argentina
4
Consejo Nacional de Investigaciones Científicas y Técnicas, Laboratorio de Canales Iónicos, Instituto de Investigaciones Médicas (IDIM), Universidad de Buenos Aires, Buenos Aires C1427ARO, Argentina
*
Author to whom correspondence should be addressed.
Received: 29 September 2018 / Revised: 27 October 2018 / Accepted: 7 November 2018 / Published: 11 November 2018
(This article belongs to the Special Issue Aquaporins)
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Abstract

Aquaporins (AQPs) function as tetrameric structures in which each monomer has its own permeable pathway. The combination of structural biology, molecular dynamics simulations, and experimental approaches has contributed to improve our knowledge of how protein conformational changes can challenge its transport capacity, rapidly altering the membrane permeability. This review is focused on evidence that highlights the functional relationship between the monomers and the tetramer. In this sense, we address AQP permeation capacity as well as regulatory mechanisms that affect the monomer, the tetramer, or tetramers combined in complex structures. We therefore explore: (i) water permeation and recent evidence on ion permeation, including the permeation pathway controversy—each monomer versus the central pore of the tetramer—and (ii) regulatory mechanisms that cannot be attributed to independent monomers. In particular, we discuss channel gating and AQPs that sense membrane tension. For the latter we propose a possible mechanism that includes the monomer (slight changes of pore shape, the number of possible H-bonds between water molecules and pore-lining residues) and the tetramer (interactions among monomers and a positive cooperative effect). View Full-Text
Keywords: water channel; osmotic permeability; gating; cooperative mechanism water channel; osmotic permeability; gating; cooperative mechanism
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Ozu, M.; Galizia, L.; Acuña, C.; Amodeo, G. Aquaporins: More Than Functional Monomers in a Tetrameric Arrangement. Cells 2018, 7, 209.

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