Revealing the Transport Cycle Dynamics of the Sodium Dependent Sugar Transporter by Double Electron-Electron Resonance and Wide-Angle X-ray Scattering

Dietary sugars have an immense importance in the metabolism of all cells. As such, it is vital to understand their cellular entry and exit pathways through specific transporters. Our research focuses on the sodium dependent sugar transporter from Vibrio parahemolyticus (vSGLT). Currently, this is the best structural model system for the mammalian transporters, which are responsible for sugar absorption in the intestine and reabsorption in the kidney. Recently, this transporter has been the target of various drugs that lower blood-sugar levels by inhibiting sugar reabsorption in the kidney.SGLTs are highly dynamic and switch between a number of conformations to facilitate sugar passage across the cell membrane. There are currently two available x-ray structures for vSGLT in an inward-occluded1 and an inward-open2 conformation. These two distinct conformations have fundamentally advanced our understanding of sugar transport to an atomic level, but did not encapsulate the dynamics of transport, nor the nature of the outward-open conformation.In order to gain further insight into the ligand dependent dynamics of vSGLT, we have conducted double electron-electron resonance (DEER) and wide-angle x-ray scattering (WAXS) studies under three conditions, each favoring different conformers in the protein: in the absence of sodium and galactose, in the presence of sodium only and in the presence of both sodium and galactose.We will discuss the overall insights gained by these two approaches, the similarities and differences with other transporters that share the Leu-T fold and the structural refinement that included combined energy terms from DEER and WAXS.1. Faham et al., (2008) Science 321(5890).2. Watanabe et al., (2010) Nature 468.