Membrane tension as a physiological mechanism that modulates water permeability in human Aquaporin 1

ROXANA TORIANO; PABLO ROSI; FLORENCIA COSTA ALMAR; MARYANT PAREDES; MARIELA LENZE; MARCELO OZU; RICARDO DORR

Salto

Congreso; Latin American Crosstalk in Biophysics and Physiology; 2015

Seccional Biofísica de la Sociedad Uruguaya de Biociencias y Sociedad Argentina de Biofísica

The Aquaporins (AQPs) are a family of tetrameric membrane integral proteins which facilitate water transport across the cell membrane. Each monomer of AQPs contains a water channel. Our former in vitro results showed that human AQP1 (hAQP1) is regulated by increments in membrane tension (1). Our present goal was to study conformational changes in hAQP1 structure as a putative physiological way to modify water permeability in cells. In silico experiments were performed by Molecular Dynamics Simulations (MDS), using PDB templates of two hAQP1 structures deposited in Protein Data Bank under codes 1FQY and 4CSK: 3.8 Å resolution 1FQY structure solved by electron crystallography containing 269 residues (2) and 3.28 Å resolution 4CSK structured solved by X-ray diffraction containing 292 residues (3). MDS experiments (50ns in explicit aqueous solvent) were carried out under two different conditions: unrestricted and restricted α-Carbon. In this latter one, only α-Carbons in the lipophilic region of the monomers were fixed thus this condition resembles the anchoring of the protein in the cellular membrane. Both the isolated monomer and the monomer inside the tetramers were studied. To analyze the water channel profile along dynamic experiments we used the PoreWalker server. Furthermore, structural descriptors -the distances between specific residues located either in the selectivity region of the pore or in the NPA site or residues between loop A and the NPA site and between loop A and the central pore of the tetramer- were used to evaluate conformational changes. Conclusions: The tetrameric conformation maintains the structure and functionality of each monomer which might have an independent behavior regarding water movement. Environmental influences can cause conformational changes that might modulate water permeability eventhough AQP1 was described as a constitutively open channel Loops A interact with their neighbor monomers and they move in the tetramer independently from each other.[1] Ozu M, Dorr RA, Gutiérrez F, Politi MT and Toriano R. Biophysical Journal 104:85?95. 2013. [2] Murata K., Nature 407: 599-605, 2000. [3] Ruiz Carrillo D. et al. Acta Crystallogr.,Sect.F 70: 1657, 2014.