Abstract
Membrane co-transport proteins that use a five-helix inverted repeat motif have recently emerged as one of the largest structural classes of secondary active transporters. However, despite many structural advances there is no clear evidence of how ion and substrate transport are coupled. Here we report a comprehensive study of the sodium/galactose transporter from Vibrio parahaemolyticus (vSGLT), consisting of molecular dynamics simulations, biochemical characterization and a new crystal structure of the inward-open conformation at a resolution of 2.7ĝ€‰Ã. Our data show that sodium exit causes a reorientation of transmembrane helix 1 that opens an inner gate required for substrate exit, and also triggers minor rigid-body movements in two sets of transmembrane helical bundles. This cascade of events, initiated by sodium release, ensures proper timing of ion and substrate release. Once set in motion, these molecular changes weaken substrate binding to the transporter and allow galactose readily to enter the intracellular space. Additionally, we identify an allosteric pathway between the sodium-binding sites, the unwound portion of transmembrane helix 1 and the substrate-binding site that is essential in the coupling of co-transport.
| Original language | English |
|---|---|
| Pages (from-to) | 988-991 |
| Number of pages | 4 |
| Journal | Nature |
| Volume | 468 |
| Issue number | 7326 |
| DOIs | |
| State | Published - 16 Dec 2010 |
Bibliographical note
Funding Information:Acknowledgements We thank T. Vondriska and K. Philipson as well as members of the Abramson, Wright and Grabe labs for useful discussions and for reading the manuscript.Wewould alsoliketothankS. Fahamfor contributions atthe early stages of this work, S. Iwata for advance release of the Mhp1 coordinates (Protein Data Bank ID, 2X79), and R. Roskies for assistance with the computations. Simulations were carried out through a TeraGrid grant at the Pittsburgh Supercomputing Center and the Texas Advanced Computing Center. This work was supported by NIH grants GM078844 (J.A.), RGY0069 (J.A.) and DK19567 (E.M.W.), and a grant from the Human Frontier Science Program (J.A.). M.G. is an Alfred P. Sloan Research Fellow.