期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1999
卷号：96
期号：13
页码：7190-7195
DOI：10.1073/pnas.96.13.7190
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：AcrAB is a constitutively expressed, major multidrug efflux system of Escherichia coli. We have purified the cytoplasmic membrane component, AcrB, to near homogeneity, and reconstituted the protein into proteoliposomes. In the presence of {Delta}pH (outside acid), the protein catalyzed the extrusion of fluorescent phospholipids, which were then trapped by protein-free acceptor vesicles. Known substrates of AcrAB, such as bile acids, erythromycin, and cloxacillin, inhibited this activity. Addition of various drugs to AcrB-containing proteoliposomes, in the presence of {Delta}pH (inside acid) resulted in proton efflux, suggesting that AcrB is a proton antiporter. Interestingly, fluorescent lipid extrusion was accelerated strongly by the periplasmic protein AcrA in the presence of Mg2+, and at pH 5.0 AcrA alone produced a slow mixing of lipids of different vesicles, without causing the mixing of intravesicular material. These results suggest that AcrA brings two membranes together, and under certain conditions may even cause the fusion of at least the outer leaflets of the membranes, contributing to the ability of the AcrAB-TolC system to pump drugs out directly into the medium.
