Crystal structure of the multidrug transporter P-glycoprotein from Caenorhabditis elegans

摘要

P-glycoprotein (P-gp) is an ATP-binding cassette transporter that confers multidrug resistance in cancer cells~(1,2) It also affects the absorption, distribution and clearance of cancer-unrelated drugs and xenobiotics. For these reasons, the structure and function of P-gp have been studied extensively for decades~3. Here we present biochemical characterization of P-gp from Caenorhabditis elegans and its crystal structure at a resolution of 3.4 angstroms. We find that the apparent affinities of P-gp for anticancer drugs actinomycin D and paclitaxel are approximately 4,000 and 100 times higher, respectively, in the membrane bilayer than in detergent. This affinity enhancement highlights the importance of membrane partitioning when a drug accesses the transporter in the membrane~4. Furthermore, the transporter in the crystal structure opens its drug pathway at the level of the membrane's inner leaflet. In the helices flanking the opening to the membrane, we observe extended loops that may mediate drug binding, function as hinges to gate the pathway or both. We also find that the interface between the transmem-brane and nudeotide-binding domains, which couples ATP hydrolysis to transport, contains a ball-and-socket joint and salt bridges similar to the ATP-binding cassette importers~5, suggesting that ATP-binding cassette exporters and importers may use similar mechanisms to achieve alternating access for transport. Finally, a model of human P-gp derived from the structure of C. elegans P-gp not only is compatible with decades of biochemical analysis~(6-12), but also helps to explain perplexing functional data regarding the Phe335Ala mutant~(13,14). These results increase our understanding of the structure and function of this important molecule.%ABC(ATP—binding cassette)转运蛋白“P-糖蛋白”在癌细胞中产生多药物抗性。本文作者在生化上和结构上对来自线虫的“P-糖蛋白”进行了定性，并用该信息生成一个人“P-糖蛋白”的同源模型。他们的数据反映了“P-糖蛋白”是怎样利用来自ATP水解的能量将亲脂性分子从细胞膜的内叶驱赶出去的。