ATP-binding cassette (ABC) transporters couple ATP hydrolysis to substrate transport across biological membranes. Although many are promising drug targets, their mechanisms of modulation by small molecule inhibitors remain largely unknown. Intriguingly, two first-generation inhibitors of the MsbA transporter, TBT1 and G247, induce opposite effects on ATP hydrolysis. Using single-particle cryo-electron microscopy and functional assays, we show that TBT1 and G247 bind adjacent yet separate pockets in the MsbA transmembrane domains. Two TBT1 molecules asymmetrically occupy the substrate binding site, leading to a collapsed inward-facing conformation with decreased distance between the nucleotide-binding domains (NBDs). In contrast, two G247 molecules symmetrically increases NBD distance in a wide inward-open state of MsbA. The divergent mechanisms of action of these MsbA inhibitors provide important insights into ABC transporter pharmacology.

中文翻译：

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第一代 MsbA 抑制剂的独特变构机制

ATP 结合盒 (ABC) 转运蛋白将 ATP 水解与跨生物膜的底物转运结合起来。尽管许多是有前途的药物靶点，但它们通过小分子抑制剂调节的机制仍然很大程度上未知。有趣的是，MsbA 转运蛋白的两种第一代抑制剂 TBT1 和 G247 对 ATP 水解产生相反的作用。使用单粒子低温电子显微镜和功能分析，我们显示 TBT1 和 G247 结合 MsbA 跨膜结构域中相邻但独立的口袋。两个 TBT1 分子不对称地占据底物结合位点，导致内向构象塌陷，核苷酸结合域 (NBD) 之间的距离减小。相比之下，两个 G247 分子在 MsbA 的宽向内开放状态下对称地增加 NBD 距离。