Mechanical gating in the FaPIP2;1 plant aquaporin would be related to structural changes in the single file region

CAVIGLIA, AGUSTÍN F.; ESPINOZA MUÑOZ, NICOLÁS; GONZÁLEZ, CARLOS; AMODEO, GABRIELA; GARATE, JOSÉ ANTONIO; OZU, MARCELO

Rosario

Congreso; L Reunión Anual de la Sociedad Argentina de Biofísica; 2022

Sociedad Argentina de Biofísica

Water permeability in aquaporins (AQPs) isdetermined by conduction through four monomers. The constitutive ΔG for waterpermeation through each one is almost equal to its self-diffusion in bulk; so,rapid control of osmotic permeability in these proteins is related to variousgating closure mechanisms. Non-linear decrease of the osmotic permeabilitycoefficient (Pf) was experimentally verified in response tomembrane tension (θ) increments in animal and plant AQPs expressed in Xenopusoocytes. To describe the underlying mechanism, we performed Molecular DynamicsSimulations on the mechanosensitive AQP of strawberry fruit FaPIP2;1 withincreasing levels of θ in the range of 0 to 50 mN m-1. Toassess the functional response of FaPIP2;1, the permeation events (PE) and theunitary osmotic permeation coefficient (pf) was quantified. pfwas estimated by segments of the channel using the pf-matrixmethod. Conformational changes were calculated by interatomic distances anddihedral angles changes, and by radii measures using HOLE2. Water load of thechannel was also counted. Our results show that pf decreasesabout two to three times with θ50 = 50 mN m-1:1.47 x10-14 ±6.66 x10-15 (θc=0 mN m-1)to 6.61 x10-15 ± 5.65 x10-15 cm3 s-1(θ50); and PE decay from 318±36 (θc) to60±52 [xmolecules s-1](θ50).Moreover, the pf-matrix suggests that the most sensitiveregion of the channel is located around the residue Isoleucine 106 next to theNPA motif. In this ~3Å length region, a ~26 fold drop of local pfwas observed (from 5.19 x10-13 ±2.59 x10-13 to 1.95 x10-14±9.25 x10-15 cm3 s-1). The load of the channeldecreased from 10.8±0.1 to 8.9±1.0 molecules. Structure changes involvediscrete movements of Ile-106 toward the lumen of the channel, which correlatesto a 1Å or less pore radius and to 45° to 180° changes in backbone dihedralangles from residue 96 to 106. Although no definitive conclusions can be madedue to large variability between monomers in each tetramer -which suggestimportant interaction effects-, these results are in line to experimentalrecords and suggest that the mechanosensitivity of FaPIP2;1 relay on torsionalmovements of the loop B which produce a narrowing of the cytoplasmic region ofthe channel via reorientation of the Ile-106 side chain.