Enhancement of proton conductance by mutations of the selectivity filter of aquaporin-1

TY - JOUR

T1 - Enhancement of proton conductance by mutations of the selectivity filter of aquaporin-1

AU - Li, Hui

AU - Chen, Hanning

AU - Steinbronn, Christina

AU - Wu, Binghua

AU - Beitz, Eric

AU - Zeuthen, Thomas

AU - Voth, Gregory A

N1 - Copyright © 2011 Elsevier Ltd. All rights reserved.

PY - 2011/4/8

Y1 - 2011/4/8

N2 - Prevention of cation permeation in wild-type aquaporin-1 (AQP1) is believed to be associated with the Asn-Pro-Ala (NPA) region and the aromatic/arginine selectivity filter (SF) domain. Previous work has suggested that the NPA region helps to impede proton permeation due to the protein backbone collective macrodipoles that create an environment favoring a directionally discontinuous channel hydrogen-bonded water chain and a large electrostatic barrier. The SF domain contributes to the proton permeation barrier by a spatial restriction mechanism and direct electrostatic interactions. To further explore these various effects, the free-energy barriers and the maximum cation conductance for the permeation of various cations through the AQP1-R195V and AQP1-R195S mutants are predicted computationally. The cations studied included the hydrated excess proton that utilizes the Grotthuss shuttling mechanism, a model "classical" charge localized hydronium cation that exhibits no Grotthuss shuttling, and a sodium cation. The hydrated excess proton was simulated using a specialized multi-state molecular dynamics method including a proper physical treatment of the proton shuttling and charge defect delocalization. Both AQP1 mutants exhibit a surprising cooperative effect leading to a reduction in the free-energy barrier for proton permeation around the NPA region due to altered water configurations in the SF region, with AQP1-R195S having a higher conductance than AQP1-R195V. The theoretical predictions are experimentally confirmed in wild-type AQP1 and the mutants expressed in Xenopus oocytes. The combined results suggest that the SF domain is a specialized structure that has evolved to impede proton permeation in aquaporins.

AB - Prevention of cation permeation in wild-type aquaporin-1 (AQP1) is believed to be associated with the Asn-Pro-Ala (NPA) region and the aromatic/arginine selectivity filter (SF) domain. Previous work has suggested that the NPA region helps to impede proton permeation due to the protein backbone collective macrodipoles that create an environment favoring a directionally discontinuous channel hydrogen-bonded water chain and a large electrostatic barrier. The SF domain contributes to the proton permeation barrier by a spatial restriction mechanism and direct electrostatic interactions. To further explore these various effects, the free-energy barriers and the maximum cation conductance for the permeation of various cations through the AQP1-R195V and AQP1-R195S mutants are predicted computationally. The cations studied included the hydrated excess proton that utilizes the Grotthuss shuttling mechanism, a model "classical" charge localized hydronium cation that exhibits no Grotthuss shuttling, and a sodium cation. The hydrated excess proton was simulated using a specialized multi-state molecular dynamics method including a proper physical treatment of the proton shuttling and charge defect delocalization. Both AQP1 mutants exhibit a surprising cooperative effect leading to a reduction in the free-energy barrier for proton permeation around the NPA region due to altered water configurations in the SF region, with AQP1-R195S having a higher conductance than AQP1-R195V. The theoretical predictions are experimentally confirmed in wild-type AQP1 and the mutants expressed in Xenopus oocytes. The combined results suggest that the SF domain is a specialized structure that has evolved to impede proton permeation in aquaporins.

KW - Animals

KW - Aquaporin 1

KW - Cations

KW - Cloning, Molecular

KW - Computational Biology

KW - Computer Simulation

KW - Gene Expression

KW - Models, Molecular

KW - Mutant Proteins

KW - Mutation, Missense

KW - Oocytes

KW - Protein Structure, Tertiary

KW - Protons

KW - Static Electricity

KW - Xenopus

U2 - 10.1016/j.jmb.2011.01.036

DO - 10.1016/j.jmb.2011.01.036

M3 - Journal article

C2 - 21277313

SN - 0022-2836

VL - 407

SP - 607

EP - 620

JO - Journal of Molecular Biology

JF - Journal of Molecular Biology

IS - 4

ER -