ATP-binding cassette (ABC) transporters use the energy of ATP hydrolysis to move molecules through cellular membranes. They are directly linked to human diseases, cancer multidrug resistance, and bacterial virulence. Very little is known of the conformational dynamics of ABC transporters, especially at the single-molecule level. Here, we combine single-molecule spectroscopy and a novel molecular simulation approach to investigate the conformational dynamics of the ABC transporter BtuCD. We observe a single dominant population of molecules in each step of the transport cycle and tight coupling between conformational transitions and ligand binding. We uncover transient conformational changes that allow substrate to enter the transporter. This is followed by a ‘squeezing’ motion propagating from the extracellular to the intracellular side of the translocation cavity. This coordinated sequence of events provides a mechanism for the unidirectional transport of vitamin B₁₂ by BtuCD.

ATP结合盒（ABC）转运蛋白利用ATP水解的能量使分子穿过细胞膜。它们与人类疾病，癌症多药耐药性和细菌毒力直接相关。人们对ABC转运蛋白的构象动力学知之甚少，尤其是在单分子水平上。在这里，我们结合单分子光谱学和一种新颖的分子模拟方法来研究ABC转运蛋白BtuCD的构象动力学。我们在运输周期的每个步骤中观察到一个单一的主要分子种群，并且构象转变和配体结合之间紧密结合。我们发现了瞬态构象变化，该变化允许底物进入转运蛋白。这之后是从移位腔的细胞外到细胞内传播的“挤压”运动。这种协调的事件顺序为维生素B的单向运输提供了一种机制BtuCD的₁₂。