Rosenberg M F, Mao Q, Holzenburg A, Ford R C, Deeley R G, Cole S P
Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology, Manchester M60 1QD, United Kingdom.
J Biol Chem. 2001 May 11;276(19):16076-82. doi: 10.1074/jbc.M100176200. Epub 2001 Jan 22.
Multidrug resistance protein 1 (MRP1/ABCC1) is an ATP-binding cassette (ABC) polytopic membrane transporter of considerable clinical importance that confers multidrug resistance on tumor cells by reducing drug accumulation by active efflux. MRP1 is also an efficient transporter of conjugated organic anions. Like other ABC proteins, including the drug resistance conferring 170-kDa P-glycoprotein (ABCB1), the 190-kDa MRP1 has a core structure consisting of two membrane-spanning domains (MSDs), each followed by a nucleotide binding domain (NBD). However, unlike P-glycoprotein and most other ABC superfamily members, MRP1 contains a third MSD with five predicted transmembrane segments with an extracytosolic NH(2) terminus. Moreover, the two nucleotide-binding domains of MRP1 are considerably more divergent than those of P-glycoprotein. In the present study, the first structural details of MRP1 purified from drug-resistant lung cancer cells have been obtained by electron microscopy of negatively stained single particles and two-dimensional crystals formed after reconstitution of purified protein with lipids. The crystals display p2 symmetry with a single dimer of MRP1 in the unit cell. The overall dimensions of the MRP1 monomer are approximately 80 x 100 A. The MRP1 monomer shows some pseudo-2-fold symmetry in projection, and in some orientations of the detergent-solubilized particles, displays a stain filled depression (putative pore) appearing toward the center of the molecule, presumably to enable transport of substrates. These data represent the first structural information of this transporter to approximately 22-A resolution and provide direct structural evidence for a dimeric association of the transporter in a reconstituted lipid bilayer.
多药耐药蛋白1（MRP1/ABCC1）是一种具有重要临床意义的ATP结合盒（ABC）多跨膜转运蛋白，它通过主动外排减少药物蓄积，从而赋予肿瘤细胞多药耐药性。MRP1也是一种有效的共轭有机阴离子转运蛋白。与其他ABC蛋白一样，包括赋予耐药性的170-kDa P-糖蛋白（ABCB1），190-kDa的MRP1具有一个核心结构，由两个跨膜结构域（MSD）组成，每个跨膜结构域后面跟着一个核苷酸结合结构域（NBD）。然而，与P-糖蛋白和大多数其他ABC超家族成员不同，MRP1包含第三个MSD，有五个预测的跨膜片段，其NH(2)末端位于胞外。此外，MRP1的两个核苷酸结合结构域比P-糖蛋白的两个核苷酸结合结构域差异大得多。在本研究中，通过对负染单颗粒和纯化蛋白与脂质重构后形成的二维晶体进行电子显微镜观察，获得了从耐药肺癌细胞中纯化的MRP1的首个结构细节。这些晶体显示p2对称性，晶胞中有一个MRP1二聚体。MRP1单体的整体尺寸约为80×100 Å。MRP1单体在投影中显示出一些假2倍对称性，在去污剂溶解颗粒的某些方向上，显示出一个朝向分子中心的充满染色剂的凹陷（假定的孔），大概是为了使底物能够转运。这些数据代表了该转运蛋白到约22 Å分辨率的首个结构信息，并为该转运蛋白在重构脂质双分子层中的二聚体缔合提供了直接的结构证据。
