在有一个 “LeuT-fold”的膜蛋白中，不清楚离子和基质运输是怎样耦合的。Watanabe等人介绍了对来自“副溶血性弧菌”的钠/半乳糖运输子(vSGLT)的结构和生化性质所做的一项综合研究以及“向内开放的”一种构型的一个新的晶体结构。这些实验表明，钠退出引起 “跨膜螺旋结构-1”发生重新取向，开启了基质退出所需的一个“内门”，同时也触发了两组“跨膜螺旋束”中的小刚体运动。这种构型变化级联决定离子和基质释放的正确时机。（生物谷Bioon.com）
生物谷推荐原文出处：
Nature doi:10.1038/nature09580
The mechanism of sodium and substrate release from the binding pocket of vSGLT
Akira Watanabe,Seungho Choe,Vincent Chaptal,John M. Rosenberg,Ernest M. Wright,Michael Grabe& Jeff Abramson
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 transporters1, 2. 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 2.7??. 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.
