Abstract
Sodium-glucose transporters (SGLTs) facilitate the movement of water across the cell membrane, playing a central role in cellular homeostasis. Here, we present a detailed analysis of the mechanism of water permeation through the inward-facing state of vSGLT based on nearly 10 μs of molecular dynamics simulations. These simulations reveal the transient formation of a continuous water channel through the transporter that permits water to permeate the protein. Trajectories in which spontaneous release of galactose is observed, as well as those in which galactose remains in the binding site, show that the permeation rate, although modulated by substrate occupancy, is not tightly coupled to substrate release. Using a, to our knowledge, novel channel-detection algorithm, we identify the key residues that control water flow through the transporter and show that solvent gating is regulated by side-chain motions in a small number of residues on the extracellular face. A sequence alignment reveals the presence of two insertion sites in mammalian SGLTs that flank these outer-gate residues. We hypothesize that the absence of these sites in vSGLT may account for the high water permeability values for vSGLT determined via simulation compared to the lower experimental estimates for mammalian SGLT1.
| Original language | English |
|---|---|
| Pages (from-to) | 1280-1289 |
| Number of pages | 10 |
| Journal | Biophysical Journal |
| Volume | 106 |
| Issue number | 6 |
| DOIs | |
| State | Published - 18 Mar 2014 |
Bibliographical note
Funding Information:We thank Shannon McCullough and Ambika Ramesh for their initial analysis on this project. Simulations were performed on the Anton special-purpose supercomputer provided by the National Resource for Biomedical Supercomputing (NRBSC), the Pittsburgh Supercomputing Center (PSC), and the Biomedical Technology Research Center for Multiscale Modeling of Biological Systems (MMBioS) through grant P41GM103712-S1 from the National Institutes of Health and grant PSCA00015P (M.G.). The Anton machine at NRBSC/PSC was generously made available by D. E. Shaw Research.
Funding Information:
This work was supported by National Institutes of Health (NIH) grants GM089740-01A1 (M.G. and J.M.R.), T32-DK061296 (J.L.A.), DK19567 (E.M.W.), and GM078844 (J.A.). The work of S.C. was supported by a start-up fund from the Daegu Gyeongbuk Institute of Science and Technology.