Abstract

Sodium/glucose and galactose transporters (SGLTs) are transmembrane proteins responsible for glucose absorption in the small intestine, uptake across the blood-brain barrier, and reabsorption in the kidney. This makes them ideal drug targets for a number of diseases including diabetes and depression. To better understand the mechanism of transport in SGLTs we examined the conformational changes that occur in vSGLT, a Vibrio cholerae homolog of human SGLT, by using double electron-electron resonance (DEER). DEER is a solution-based NMR technique which measures the distances between tagged amino acids in a protein. The DEER measurements for several mutants that targeted transmembrane helices 4, 6, 7, and 9 show that the distances between the helices on the intracellular face of vSGLT decrease when sodium and galactose are bound as compared to the unbound protein. These data lend further support to the hypothesis that vSGLT utilizes the alternating access mechanism of substrate transport during which the binding of a substrate causes a conformational change that allows the substrate access to the opposite face of the protein.