Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute, Netherlands Proteomics Centre and Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Structure. 2013 May 7;21(5):861-7. doi: 10.1016/j.str.2013.03.007. Epub 2013 Apr 18.
Energy coupling factor (ECF) transporters are a recently discovered class of ABC transporters that mediate vitamin uptake in prokaryotes. Characteristic for ECF-type ABC transporters are small integral membrane proteins (S-components) that bind the transported substrates with high affinity. S-components associate with a second membrane protein (EcfT) and two peripheral ATPases to form a complete ATP-dependent transporter. Here, we have used EPR spectroscopy, stopped-flow fluorescence spectroscopy, and molecular dynamics simulations to determine the structural rearrangements that take place in the S-component ThiT from Lactococcus lactis upon binding of thiamin. Thiamin-induced conformational changes were confined to the long and partially membrane-embedded loop between transmembrane helices 1 and 2 that acts as a lid to occlude the binding site. The results indicate that solitary ThiT functions as a bona fide high-affinity substrate binding protein, which lacks a translocation pathway within the protein.
能量偶联因子（ECF）转运蛋白是一类最近发现的 ABC 转运蛋白，可介导原核生物对维生素的摄取。ECF 型 ABC 转运蛋白的特征是与运输底物具有高亲和力结合的小整合膜蛋白（S 成分）。S 成分与第二种膜蛋白（EcfT）和两个外周 ATP 酶结合，形成完整的 ATP 依赖性转运体。在这里，我们使用电子顺磁共振波谱、停流荧光光谱和分子动力学模拟来确定乳球菌 lactis 中的 ThiT 结合硫胺素时发生的结构重排。硫胺素诱导的构象变化仅限于跨膜螺旋 1 和 2 之间的长的、部分嵌入膜的环，该环充当盖子以封闭结合位点。结果表明，孤立的 ThiT 作为一种真正的高亲和力底物结合蛋白发挥作用，该蛋白在蛋白质内缺乏转运途径。
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