van Veen H W, Venema K, Bolhuis H, Oussenko I, Kok J, Poolman B, Driessen A J, Konings W N
Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Haren, The Netherlands.
Proc Natl Acad Sci U S A. 1996 Oct 1;93(20):10668-72. doi: 10.1073/pnas.93.20.10668.
Resistance of Lactococcus lactis to cytotoxic compounds shares features with the multidrug resistance phenotype of mammalian tumor cells. Here, we report the gene cloning and functional characterization in Escherichia coli of LmrA, a lactococcal structural and functional homolog of the human multidrug resistance P-glycoprotein MDR1. LmrA is a 590-aa polypeptide that has a putative topology of six alpha-helical transmembrane segments in the N-terminal hydrophobic domain, followed by a hydrophilic domain containing the ATP-binding site. LmrA is similar to each of the two halves of MDR1 and may function as a homodimer. The sequence conservation between LmrA and MDR1 includes particular regions in the transmembrane domains and connecting loops, which, in MDR1 and the MDR1 homologs in other mammalian species, have been implicated as determinants of drug recognition and binding. LmrA and MDR1 extrude a similar spectrum of amphiphilic cationic compounds, and the activity of both systems is reversed by reserpine and verapamil. As LmrA can be functionally expressed in E. coli, it offers a useful prokaryotic model for future studies on the molecular mechanism of MDR1-like multidrug transporters.
乳酸乳球菌对细胞毒性化合物的抗性与哺乳动物肿瘤细胞的多药耐药表型具有共同特征。在此，我们报道了LmrA（人多药耐药P-糖蛋白MDR1的乳球菌结构和功能同源物）在大肠杆菌中的基因克隆及功能特性。LmrA是一种590个氨基酸的多肽，在N端疏水结构域具有六个α-螺旋跨膜片段的假定拓扑结构，其后是一个包含ATP结合位点的亲水结构域。LmrA与MDR1的两个半部分相似，可能作为同型二聚体发挥作用。LmrA与MDR1之间的序列保守性包括跨膜结构域和连接环中的特定区域，在MDR1及其他哺乳动物物种中的MDR1同源物中，这些区域被认为是药物识别和结合的决定因素。LmrA和MDR1排出相似谱的两亲性阳离子化合物，并且两种系统的活性都被利血平和维拉帕米逆转。由于LmrA可以在大肠杆菌中功能性表达，它为未来研究MDR1样多药转运蛋白的分子机制提供了一个有用的原核模型。
