title: Trimeric ring-like structure of ArsA ATPase.
abstract: ArsA protein is the soluble subunit of the Ars anion pump in the Escherichia coli membrane which extrudes arsenite or antimonite from the cytoplasm. The molecular weight of the subunit is 63 kDa. In the cell it hydrolyzes ATP, and the energy released is used by the membrane-bound subunit ArsB to transport the substrates across the membrane. We have obtained two-dimensional crystals of ArsA in the presence of arsenite on negatively-charged lipid monolayer composed of DMPS and DOPC. These crystals have been studied using electron microscopy of negatively-stained specimens followed by image processing. The projection map obtained at 2.4 nm resolution reveals a ring-like structure with threefold symmetry. Many molecular assemblies with the same ring-shape and dimensions were also seen dispersed on electron microscopy grids, prepared directly from purified ArsA protein solution. Size-exclusion chromatography of the protein sample with arsenite present revealed that the majority of the protein particles in solution have a molecular weight of about 180 kDa. Based on these experiments, we conclude that in solution the ArsA ATPase with substrate bound is mainly in a trimeric form.
authors.affiliation: State Key Laboratory of Biomembrane & Membrane Biotechnology, Department of Biological Sciences & Biotechnology, Tsinghua University, Beijing, PR China.
authors.forename: H W
authors.initials: HW
authors.lastname: Wang
authors.forename: Y J
authors.initials: YJ
authors.lastname: Lu
authors.forename: L J
authors.initials: LJ
authors.lastname: Li
authors.forename: S
authors.initials: S
authors.lastname: Liu
authors.forename: D N
authors.initials: DN
authors.lastname: Wang
authors.forename: S
authors.initials: S
authors.lastname: Sui
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000648:ultrastructure; D053501:Arsenite Transporting ATPases; D018053:Arsenites / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000648:ultrastructure; D002850:Chromatography, Gel; D003460:Crystallization; D004926:Escherichia coli; D007091:Image Processing, Computer-Assisted; D016623:Ion Pumps; D008565:Membrane Proteins / Q000737:chemistry* / Q000648:ultrastructure; D008854:Microscopy, Electron; D009097:Multienzyme Complexes; D010713:Phosphatidylcholines / Q000737:chemistry; D011487:Protein Conformation; D014494:Unithiol / Q000737:chemistry
chemical_list: D018053:Arsenites; D001426:Bacterial Proteins; D016623:Ion Pumps; D008565:Membrane Proteins; D009097:Multienzyme Complexes; D010713:Phosphatidylcholines; D014494:Unithiol; D000251:Adenosine Triphosphatases; D053501:Arsenite Transporting ATPases; C017251:1,2-oleoylphosphatidylcholine; C015001:arsenite