Energetics of Urea Permeation through Sodium-Dependent Galactose Cotransporter vSGLT


In human kidneys, the glomeruli filter about 54 g of urea from the blood each day and approximately 12-14 g of which is reabsorbed in the proximal tubule that is believed to be devoid of urea channels or uniporters. Experimental evidence suggests that human sodium-dependent glucose cotransporters (hSGLTs) may be involved in urea uptake. Our Molecular dynamics (MD) simulations with the inward-facing structure of vSGLT (PDB ID: 3DH4) resulted in permeation of a single urea molecule in presence of a bound galactose. Separately, long-timescale MD simulations (1.5 ms) performed on the Anton supercomputer in presence of urea did not result in any urea permeation event. During these simulations, sugar was observed to escape the binging pocket indicating that the presence of galctose in the binding pocket may facilitate urea escape to the periplasm. Here we present our results on the study of energetics of urea transport along the previously observed pathway. Umbrella sampling simulations are performed to calculate the potential of mean force (PMF) of urea exit. Separate sets of umbrella sampling simulations are performed in presence and absence of a bound galactose to investigate our hypothesis that the bound galactose facilitates urea permeation. Two different force field parameters for urea are used to inspect the validity of the previously observed urea permeation event.

Biophys. J.