美国爱荷华州立大学的华裔科学家Edward Yu领导的团队最近发现了细菌体内外排泵的结晶结构，该成果有助于研究人员更好地了解细菌耐药性机制，以开发出新治疗方法消除细菌耐药性。相关结果发表在9月23日的《自然》（Nature）杂志上。
研究人员首先将大肠杆菌外排泵的组成成分――膜蛋白进行纯化、结晶，制备含有重金属铜和银的细菌样品及对照组，然后使用X射线结晶分析技术对比分析其结构，从而研究出细菌体内重金属外排机制。
研究人员在文章中特别提到CusA的结晶结构，CusA是一种内膜转运蛋白，由1,047个氨基酸残基组成，属耐药结节细胞分化（resistance-nodulation-division，RND）超家族。
“我们希望能彻底研究出这些重金属外排泵的机制”，Edward Yu表示，“如此一来，生物技术人员便可制备出相应抑制剂，消除细菌的抗生素抗性”。
推荐英文摘要：
Nature doi:10.1038/nature09395
Crystal structures of the CusA efflux pump suggest methionine-mediated metal transport
Feng Long,Chih-Chia Su,Michael T. Zimmermann,Scott E. Boyken,Kanagalaghatta R. Rajashankar,Robert L. Jernigan" Edward W.
Gram-negative bacteria, such as Escherichia coli, frequently use tripartite efflux complexes in the resistance-nodulation-cell division (RND) family to expel various toxic compounds from the cell1, 2. The efflux system CusCBA is responsible for extruding biocidal Cu(I) and Ag(I) ions3, 4. No previous structural information was available for the heavy-metal efflux (HME) subfamily of the RND efflux pumps. Here we describe the crystal structures of the inner-membrane transporter CusA in the absence and presence of bound Cu(I) or Ag(I). These CusA structures provide new structural information about the HME subfamily of RND efflux pumps. The structures suggest that the metal-binding sites, formed by a three-methionine cluster, are located within the cleft region of the periplasmic domain. This cleft is closed in the apo-CusA form but open in the CusA-Cu(I) and CusA-Ag(I) structures, which directly suggests a plausible pathway for ion export. Binding of Cu(I) and Ag(I) triggers significant conformational changes in both the periplasmic and transmembrane domains. The crystal structure indicates that CusA has, in addition to the three-methionine metal-binding site, four methionine pairs―three located in the transmembrane region and one in the periplasmic domain. Genetic analysis and transport assays suggest that CusA is capable of actively picking up metal ions from the cytosol, using these methionine pairs or clusters to bind and export metal ions. These structures suggest a stepwise shuttle mechanism for transport between these sites.
Molecular, Cellular and Developmental Biology Interdepartmental Graduate Program, Iowa State University, Iowa 50011, USA
Feng Long " Edward W. Yu
Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
Chih-Chia Su " Edward W. Yu
Bioinformatics and Computational Biology Interdepartmental Graduate Program, Iowa State University, Ames, Iowa 50011, USA
Michael T. Zimmermann, Scott E. Boyken, Robert L. Jernigan " Edward W. Yu
NE-CAT and Department of Chemistry and Chemical Biology, Cornell University, Building 436E, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, USA
Kanagalaghatta R. Rajashankar
Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA
Robert L. Jernigan " Edward W. Yu
Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
Edward W. Yu
