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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Flexibility in the ABC transporter MsbA: Alternating access with a twist
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Flexibility in the ABC transporter MsbA: Alternating access with a twist

机译：ABC转运车MsbA的灵活性：交替存取

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摘要

ATP-binding cassette (ABC) transporters are integral membrane proteins that translocate a wide variety of substrates across cellular membranes and are conserved from bacteria to humans. Here we compare four x-ray structures of the bacterial ABC lipid flip-pase, MsbA, trapped in different conformations, two nucleotide-bound structures and two in the absence of nucleotide. Comparison of the nucleotide-free conformations of MsbA reveals a flexible hinge formed by extracellular loops 2 and 3. This hinge allows the nucleotide-binding domains to disassociate while the ATP-binding half sites remain facing each other. The binding of the nucleotide causes a packing rearrangement of the transmembrane helices and changes the accessibility of the transporter from cytoplasmic (inward) facing to extracellular (outward) facing. The inward and outward openings are mediated by two different sets of transmembrane helix interactions. Altogether, the conforma-tional changes between these structures suggest that large ranges of motion may be required for substrate transport.
机译：ATP结合盒（ABC）转运蛋白是不可或缺的膜蛋白，可跨细胞膜转运多种底物，并从细菌向人类保守。在这里，我们比较了细菌ABC脂质翻转酶MsbA的四个X射线结构，它们被困在不同的构象中，两个核苷酸结合的结构和两个不存在核苷酸的结构。 MsbA的无核苷酸构象的比较揭示了由细胞外环2和3形成的柔性铰链。这种铰链允许核苷酸结合结构域解离，而ATP结合半位点保持彼此面对。核苷酸的结合导致跨膜螺旋的堆积重排，并将转运蛋白的可及性从胞质（向内）改变为细胞外（向外）。向内和向外的开口是由两组不同的跨膜螺旋相互作用介导的。总而言之，这些结构之间的构象变化表明底物传输可能需要大范围的运动。

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