Water Dynamics and Ion Interaction at Channel Entrance of Aquaporin 1

Abstract

The aquaporins (AQPs) are transmembrane water channels which exclusively transport water molecules across the plasma membranes corresponding to the osmotic gradients. At the inner part of the pore, single-file water permeation obeys a non-Poisson process attributed to 1/f fluctuations of amino acids [1]. Recently, using finite-element calculations it is suggested that the characteristic hourglass shape of AQPs may optimize the water transportation though the AQPs [2]. The cone-shaped vestibules with suitable opening angle can make an increase of water permeability. However, molecular details of the interaction of water and ion molecules with the amino acids at the cone-shaped vestibules remain unclear. Here we use all-atom molecular dynamics simulations for a system of AQP1/lipid membrane to investigate dynamics of water and ion molecules at the con-shaped vestibules of the AQP1. Analyzing the residence time of water and ion molecules at the surface of the AQP1, we found that residence time of water molecules at the con-shaped vestibules is long, which cases the water retardation at the entrance and increase the reorientation time of water molecules. Moreover, we analyze the interaction of ions at the conical entrance.[1] E. Yamamoto et al., Phys. Rev. E 89, 022718 (2014).[2] S. Gravelle et al., Proc. Natl. Acad. Sci. USA 110, 16367 (2013).