Mechanism of Substrate Translocation in an Alternating Access Transporter.
Mechanism of Substrate Translocation in an Alternating Access Transporter.
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DOI：
10.1016/j.cell.2017.03.010
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发表时间：
2017-03-23
期刊：
影响因子：
64.5
通讯作者：
Feng L
中科院分区：
文献类型：
--
作者：
Latorraca NR;Fastman NM;Venkatakrishnan AJ;Frommer WB;Dror RO;Feng L
转运蛋白通过在不同的构象状态之间交替来使分子穿过细胞膜。关于转运蛋白如何在状态之间转换以及这种结构重排如何调节底物易位的基本问题仍然存在。在这里，我们通过晶体学和无引导分子动力学模拟捕获易位过程，提供交替访问传输的原子级描述。从此处报道的向外开放的葡萄糖结合结构起始的 SWEET 家族转运蛋白的模拟自发地采用闭塞和向内开放的构象。引人注目的是，这些构象与晶体结构相匹配，包括我们的向内开放结构。诱变实验进一步验证了模拟预测。我们的结果表明，状态转换是由细胞外和细胞内“门”关闭时形成的有利相互作用以及两个门关闭时不利的跨膜螺旋构型驱动的。这种机制导致门之间紧密的变构耦合，防止它们同时打开。有趣的是，底物似乎可以“搭便车”穿过膜，而不会引起转运蛋白的重大结构重排。
Transporters shuttle molecules across cell membranes by alternating among distinct conformational states. Fundamental questions remain about how transporters transition between states and how such structural rearrangements regulate substrate translocation. Here we capture the translocation process by crystallography and unguided molecular dynamics simulations, providing an atomic-level description of alternating access transport. Simulations of a SWEET-family transporter initiated from an outward-open, glucose-bound structure reported here spontaneously adopt occluded and inward-open conformations. Strikingly, these conformations match crystal structures, including our inward-open structure. Mutagenesis experiments further validate simulation predictions. Our results reveal that state transitions are driven by favorable interactions formed upon closure of extracellular and intracellular “gates” and by an unfavorable transmembrane helix configuration when both gates are closed. This mechanism leads to tight allosteric coupling between gates, preventing them from opening simultaneously. Interestingly, the substrate appears to take a “free ride” across the membrane without causing major structural rearrangements in the transporter.