在有一個(gè) “LeuT-fold”的膜蛋白中，不清楚離子和基質(zhì)運(yùn)輸是怎樣耦合的。Watanabe等人介紹了對(duì)來自“副溶血性弧菌”的鈉/半乳糖運(yùn)輸子(vSGLT)的結(jié)構(gòu)和生化性質(zhì)所做的一項(xiàng)綜合研究以及“向內(nèi)開放的”一種構(gòu)型的一個(gè)新的晶體結(jié)構(gòu),。這些實(shí)驗(yàn)表明,，鈉退出引起 “跨膜螺旋結(jié)構(gòu)-1”發(fā)生重新取向，開啟了基質(zhì)退出所需的一個(gè)“內(nèi)門”，同時(shí)也觸發(fā)了兩組“跨膜螺旋束”中的小剛體運(yùn)動(dòng),。這種構(gòu)型變化級(jí)聯(lián)決定離子和基質(zhì)釋放的正確時(shí)機(jī)。（生物谷Bioon.com）
生物谷推薦原文出處：
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.
