BACKGROUND P-glycoprotein (ABCB1) is an ATP-binding cassette transporter that plays an important role in the clearance of drugs and xenobiotics and is associated with multi-drug resistance in cancer. Although several P-glycoprotein structures are available, these are either at low resolution, or represent mutated and/or quiescent states of the protein. RESULTS In the post-hydrolytic state the structure of the wild-type protein has been resolved at about 8 Å resolution. The cytosolic nucleotide-binding domains (NBDs) are separated but ADP remains bound, especially at the first NBD. Gaps in the transmembrane domains (TMDs) that connect to an inner hydrophilic cavity are filled by density emerging from the annular detergent micelle. The NBD-TMD linker is partly resolved, being located between the NBDs and close to the Signature regions involved in cooperative NBD dimerization. This, and the gap-filling detergent suggest steric impediment to NBD dimerization in the post-hydrolytic state. Two central regions of density lie in two predicted drug-binding sites, implying that the protein may adventitiously bind hydrophobic substances even in the post-hydrolytic state. The previously unresolved N-terminal extension was observed, and the data suggests these 30 residues interact with the headgroup region of the lipid bilayer. CONCLUSION The structural data imply that (i) a low basal ATPase activity is ensured by steric blockers of NBD dimerization and (ii) allocrite access to the central cavity may be structurally linked to NBD dimerization, giving insights into the mechanism of drug-stimulation of P-glycoprotein activity.

中文翻译：

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水解后状态下P-糖蛋白（ABCB1）结构的新特征，分辨率为7.9Å。

背景技术P-糖蛋白（ABCB1）是一种ATP结合盒转运蛋白，在清除药物和异种生物中起重要作用，并与癌症的多药耐药性有关。尽管有几种P糖蛋白结构可用，但它们要么处于低分辨率状态，要么代表蛋白的突变和/或静态状态。结果在水解后状态下，野生型蛋白质的结构已以约8Å的分辨率解析。胞质核苷酸结合结构域（NBD）是分离的，但ADP仍保持结合状态，尤其是在第一个NBD处。连接到内部亲水腔的跨膜结构域（TMD）中的间隙被环状洗涤剂胶束中出现的密度填充。NBD-TMD链接器已部分解决，位于NBD之间，并靠近参与NBD二聚化的特征区。这和填充间隙的洗涤剂暗示了在水解后状态下NBD二聚作用的空间位阻。密度的两个中心区域位于两个预测的药物结合位点，这意味着即使在水解后的状态下，蛋白质也可能会偶然结合疏水性物质。观察到先前未解决的N-末端延伸，并且数据表明这30个残基与脂质双层的头基区域相互作用。结论：结构数据暗示（i）NBD二聚化的空间阻滞剂可确保低的基础ATPase活性，并且（ii）分配晶石进入中央腔的结构可能与NBD二聚化相关，