Human ATP-binding cassette (ABC) transporter ABCD1 transports CoA esters of saturated/monounsaturated very long chain fatty acid from cytosol to the peroxisome for β-oxidation. Dysfunction of human ABCD1 usually causes the severe progressive genetic disorder X-linked adrenoleukodystrophy, which eventually affects the adrenal glands and/or the central nervous system. Here, we report three cryo-EM structures of human ABCD1 in various states. The apo-form ABCD1 at 3.53 &Aring resolution adopts an inward-facing conformation, harboring a phosphatidyl ethanolamine (PE) molecule at each lateral entry of substrate cavity. In the substrate-bound ABCD1 structure at 3.59 &Aring resolution, two molecules of C22:0-CoA (one of the physiological substrates of ABCD1) is symmetrically bound to the transmembrane domains (TMDs). Each C22:0-CoA adopts an unpresented L-shape configuration: the CoA portion inserts into a polar pocket at the TMD at a pose parallel to the membrane plane, whereas the acyl chain portion perpendicular to membrane plane is embedded in a hydrophobic pocket at the opposite TMD. Upon binding the two C22:0-CoA molecules, which resemble a pair of hinges crossing the two TMDs, the two nucleotide-binding domains (NBDs) of ABCD1 approach towards each other. Addition ATP to the substrate-bound ABCD1 enabled us to reveal an ATP-bound structure at 2.79 &Aring, which shows an outward-facing conformation with the dimerized NBDs succeeding substrate release. These three structures combined with biochemical assays exhibit a snapshot of ABCD1-mediated substrate recognition, translocation and release. These findings provide the structural insights into the transport mechanism of ABC transporters that transport amphipathic molecules with long acyl chains.

中文翻译：

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人类 ABCD1 底物识别和易位的结构基础

人 ATP 结合盒 (ABC) 转运蛋白 ABCD1 将饱和/单不饱和极长链脂肪酸的 CoA 酯从细胞溶质转运到过氧化物酶体进行 β-氧化。人类 ABCD1 的功能障碍通常会导致严重的进行性遗传疾病 X 连锁肾上腺脑白质营养不良，最终影响肾上腺和/或中枢神经系统。在这里，我们报告了不同状态下人类 ABCD1 的三种冷冻电镜结构。3.53 & Aring 分辨率的 apo 形式 ABCD1 采用面向内的构象，在基底腔的每个横向入口处含有一个磷脂酰乙醇胺 (PE) 分子。在分辨率为 3.59 & Aring 的底物结合 ABCD1 结构中，两个 C22:0-CoA 分子（ABCD1 的生理底物之一）对称地与跨膜结构域 (TMD) 结合。每个 C22：0-CoA 采用未呈现的 L 形构型：CoA 部分以平行于膜平面的姿势插入 TMD 的极性袋中，而垂直于膜平面的酰基链部分嵌入相反 TMD 的疏水袋中. 在结合两个 C22:0-CoA 分子后，它们类似于穿过两个 TMD 的一对铰链，ABCD1 的两个核苷酸结合域 (NBD) 相互接近。将 ATP 添加到底物结合的 ABCD1 使我们能够在 2.79 Å 处揭示 ATP 结合结构，其显示出与底物释放后二聚化 NBD 的外向构象。这三种结构与生化分析相结合，展示了 ABCD1 介导的底物识别、易位和释放的快照。