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

AGUSTIN CAVIGLIA; ESPINOZA MUÑOZ, N; CARLOS GONZALEZ; AMODEO, GABRIELA; JOSE ANTONIO GARATE; OZU, MARCELO

Rosario

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

Sociedad Argentina de Biofisica

Water permeability in aquaporins (AQPs) is determined by conduction throughfour monomers. The constitutive ΔG for water permeation through each one is almostequal to its self-diffusion in bulk; so, rapid control of osmotic permeability in theseproteins is related to various gating closure mechanisms. Non-linear decrease of theosmotic permeability coefficient (Pf) was experimentally verified in response to membranetension (θ) increments in animal and plant AQPs expressed in Xenopus oocytes. Todescribe the underlying mechanism, we performed Molecular Dynamics Simulations onthe mechanosensitive AQP of strawberry fruit FaPIP2;1 with increasing levels of θ in therange of 0 to 50 mN m-1. To assess the functional response of FaPIP2;1, the permeationevents (PE) and the unitary osmotic permeation coefficient (pf) was quantified. pf wasestimated by segments of the channel using the pf-matrix method. Conformationalchanges were calculated by interatomic distances and dihedral angles changes, and byradii measures using HOLE2. Water load of the channel was also counted. Our resultsshow that pf decreases about two to three times with θ50 = 50 mN m-1: 1.47 x10-14 ±6.66x10-15 (θc=0 mN m-1) to 6.61 x10-15 ± 5.65 x10-15 cm3 s-1 (θ50); and PE decay from318±36 (θc) to 60±52 [x107molecules s-1](θ50). Moreover, the pf-matrix suggests that themost sensitive region of the channel is located around the residue Isoleucine 106 next tothe NPA motif. In this ~3Å length region, a ~26 fold drop of local pf was observed (from5.19 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 involve discretemovements of Ile-106 toward the lumen of the channel, which correlates to a 1Å or lesspore radius and to 45° to 180° changes in backbone dihedral angles from residue 96 to106. Although no definitive conclusions can be made due to large variability betweenmonomers in each tetramer -which suggest important interaction effects-, these resultsare in line to experimental records and suggest that the mechanosensitivity of FaPIP2;1relay on torsional movements of the loop B which produce a narrowing of the cytoplasmicregion of the channel via reorientation of the Ile-106 side chain.